It is surprising the number of buyers who think they want a clip-on thermal scope, and then realize what a pain in the butt the scope is and that instead of people a part of a jack of all trades sort of deal, it turns out to be a lot of compromises and hassles.
No doubt Leica is going to make a nice product. Not arguing about that at this point as nobody here (that I know of, state side) has seen one/used on in the field state side.
However, here are the problems with this particular setup as it is and as it appears in the promo images/videos
This appears to be a proprietary mating between a Leica clip-on thermal and day optic. I have not seen anything on adapters for other brands of optics. If proprietary, then you have to buy their day scope to go with the clip-on thermal. That would greatly diminish the utility of the clip-on.
Clip-ons that hang off the front of the day optic as shown in the image put a LOT of stress on the daylight scope barrel at the point of the front scope ring. Some scopes are heavy duty enough and can handle it. Lightweight scopes cannot. Even if they can under normal circumstances, you still have all that extra material hanging on the front t catch on things or otherwise be influenced when getting carried that will strong the day scope at the front scope ring point. Torque is the key problem that I am lamenting. You can avoid damage to the day scope with a clip-on that rail mounts in front of the day optic, but that has some additional issues as well.
Operating the thermal clip-on is not convenient. The bigger the day scope, the farther away all the controls are for adjustment. Maybe you are a tall guy with ape-like arms and it isn't an issue. Maybe you are a short guy and it is a huge issue.
This is especially true for the NUC (non-uniformity correction/calibration) function that has to be carried out frequently/occasionally during use. Hopefully, the Leica has a semi-auto mode where the sequence is trigger by the shooter. If it only runs in automatic mode (like units from another company), this is a real problem and safety issue because the clip-on will NUC at very in opportune times. During NUC, the screen freezes. Depending on the brand, the NUC process may take anywhere from 3/4 of a second to a couple of seconds. It doesn't sound like much until it happens just as you are pulling the trigger or during a time when you need a follow-up shot. There are numerous hog hunting videos out there where the shooters are trying to stop running hogs and either can't shoot during the freeze of the NUC, or are shooting during the freeze of the NUC despite no longer being able to see where they are actually shooting.
Leica claims their clip-on has repeatability (of zero) and it very well may (all clip-on manufacturers claim this). I think it is going to be a screw-on which is the best way for this to be. If not, then it can probably be mismounted and that means you really don't know if your zero is good until you pull the trigger. I have hunted with guys with clip-ons that all of a sudden find they can't hit anything and so we stop back at the range and find that their zero is many MOA off. They take off the unit, re-install, check zero, and it is spot-on. It is okay to trust that it will work, but the process probably should come with verification each time you remount the clip-on.
Putting and extra 1-1.5 lbs of optic forward on the rifle often "unbalances" the rifle. I am not big into the topic of rifle balance, but this is a common complaint I hear about the setup from those who are particular about how their rifles feel...and they don't like it. It does make for a definite muzzle-heavy feel. I like to think it helps with recoil.
Most to the folks that I know that have gone the clip-on route have abandoned it to go with a dedicated thermal rifle scope. The perceived flexibility advantages did not outweigh the disadvantages. Clip-ons will be great in some circumstances, such as for coyote hunters who have their nice little stands and can setup and wait, then break down everything and travel to a new location for another stand.
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Dan made some good points, but a couple I will quibble with, and I will limit discussion to traditional NV (not digital NV) and thermal.
You can walk, ride a bike, read a map, read a book, pretty much anything you can do with natural light you can do with night vision. With thermal the print on the book will be the same temp as the paper so it won’t stand out. You could also walk right into a an armadillo hole with thermal if you were trying to navigate discretely since it’s the same temperature as the surrounding ground.
You can do most things with night vision that you can do with natural light, but even with Gen III when you are under the tree canopy, you will need an IR illuminator to make night vision useful. On moonless nights, you will often need IR illuminators as well in order to make night vision useful.
I navigate with thermal all the time. Whether or not I can see an armadillo hole has to do with the heat of the ground, particularly how uniform it is, and the thermal sensitivity of the thermal optic. Thermal sensitivity is improving. Used to be that a good rain would homogenize the thermal view such that only the animals would stand out against a grey background, though the background might include a field with a few trees and backed by an entire forest. Some of the new thermals will still pick a lot of the background out into even worse thermal conditions because of improved thermal sensitivity. There still comes a point where things just look like crap, however. This is called thermal crossover.
You can see through glass with NV, but not with thermal. Depth perception is poor with NV and is terrible with thermal. You CAN read the print in a book with thermal IF you heat of the page (such as with sunlight) such that the inked letters will differentially absorb heat from the rest of the page. This is an extreme example, only noting that it isn't impossible, just hugely difficult to accomplish.
Thermal is the undisputed champion of identifying living objects!
I am going to strongly disagree with this point and reclarify it. Thermal is the undisputed champion of
spotting thermally distinct objects. Thermal is not a biosensor. It doesn't care if an object is alive or dead, only whether or not it stands out from the surroundings by being warmer or cooler. Identification is a whole other matter. You can spot things in the shadows of the night with thermal that people with night vision only wish they could see. Camo'd animals are still very much camo'd to people with night vision and equally hard to see. People transitioning from from night vision to thermal often have to go through a learning process to
interpret thermal imagery. In the civie market right now, save for a camera coming from I-ray out of China that is high definition (and about $35K and not weapon mountable - yet), the BEST resolution you get with thermal is 640x480 or 512. Zoom is digital, NOT optical. This is critical. That means your best image is at whatever native magnification you have. So if you have a 640x480 3x (native) thermal weapon sight and you double the magnification to 6x by zooming it, you are now looking at a 320x240 resolution image, or
1/4 the resolution. Every time you double the level of mag, you quarter the resolution again. Some of the military vehicle mounted thermals get around this by having a carousel of lenses of different magnifications. When they zoom, the optic literally changes the lens being used, thereby maintain the resolution and achieving true optical zoom. You don't find this on any civie handheld or weapon mountable thermals right now.
Different companies have different classifications for the differences (in pixels) between spotting a target (1 or 2 pixels), recognizing a target, and identifying a target. People do a LOT of shooting based on recognition and not actual identification. There is a difference between these levels and it can be critical. Over the years of hunting, I have confused and seen other hunters confused in trying to identify blobular targets at distance
Claimed ID ACTUAL ID
Coyote -----> Deer
Coyote -----> Jackrabbit
Coyote -----> Domestic dog (some domestics can look exactly like coyotes on thermal)
Coyote -----> Hog
Coyote -----> Fox
Bobcat -----> Coyote
Hog -----> Deer
Hog -----> Calf
Hog -----> Full size adult cow
Hog -----> Owl
Hog -----> Rock (we call these PSRs or 'pig-shaped rocks')
Hog -----> Pool of water (this is on me. I stalked a pool of water in the woods on night. The weird thing is that it appeared to move as I was trying to circle around)
Hog -----> Fawn
Deer -----> Horse
Deer -----> Hog
Deer -----> Coyote
Fawn -----> Hog
Cow -----> Horse
Calf -----> Hog
Calf -----> Deer
Fox -----> Coyote
Raccoon ------> Coyote
Bobcat ------> Raccoon
Mountain Lion -----> Domestic Cat
As hog hunters spotting animals in a field, we will often assess the animals based on behavior and general silhouette. This results on a high confirmation rate of target "identification," but is not infallible. In reality, it is often NOT identification, not initially. It is recognition in many cases until we can identify some particular trait that is absolutely diagnostic of being a particular species.
For example, to distinguish a deer or cattle or horse and a hog, we look for neck length. Long necks # hogs. A deer with its head down eating in 1 foot tall grass can look virtually exactly like a hog with its head down in 8" grass. So we wait for the animal to raise its head. You know what else has a short neck like a hog? A deer with its head turned to the side. If it raises its head while looking to the side, you will perceive the optical illusion afforded by the 2D image of there being a short neck, not necessarily where the head is turned to the side.
We look for movement. Hogs tend to move more and move differently than deer, but not always. Hogs tend to move differently than cattle, but calves and hogs are often both very active.
A buddy of mine killed a raccoon, believing it was a bobcat. He "identified" it as a bobcat based on its short tail. It was missing about half the length of its tail, but it was a raccoon, not a bobcat. Particularly at distance (within shooting distance), the two animals can be of similar size, appear to present the same basic profile, can move in similar manners, and so a shortened tail appeared to be the clincher. It wasn't. Fortunately, the landowner hated raccoons and this was not a problem, but it could have been. This was not an identified target. It was a recognized target.
I could go into a lot more detail on other reasons why thermal isn't great for 'identification' but that would be beating a dead horse. A lot of the problems with thermal "identifications" can be rectified by getting in close. All the really amazing thermal images manufacturers use to sell their products are typically inside of 50 yards and often inside of 25 yards. The animals look absolutely amazing at those distances, even on many lower resolution thermal units. Honestly, however, if I have gotten as close as some of the ad images, I have already assessed the animal based on non-visual criteria such as sounds and smells.
I do believe that for hunters, thermal does offer a significantly higher level of utility for spotting and then closing and identifying (versus just recognizing) prey. It is the king of spotting. It may be the king of recognition. In the right circumstances, it is great for identification, but often it really isn't and a lot of interpretation is applied to understand what the person is seeing.
