I have the MK390 rifle scope and two other Gen II monoculars, one of which is the ATN Night Spirit. I have used the monoculars with IR compatible Aimpoint red dot sights with good results, but all within 50 yards so far.
Of the three, the MK390 has the poorest light gathering abilities, though shockingly, it has the clearest and most defined image. The image quality really is much better than the other scopes. As a Gen I scope, it is fairly large and bulky.
The IR illuminator on the MK390 is ATN's removeable long range illuminator (IR450). By long range, it is better than several of the built-in illuminators I have seen on various scopes. The IR illuminators on my Gen II scopes are really for very short range viewing, not really more than 20-30 yards of good illumination.
With the MK390's illuminator, I can see dark objects fairly well out to 50 yards and light object out to about 75.
The MK390 is cheap compared to Gen II scopes that start at about $999 for monoculars and $1500 or so for Gen II rifle scopes.
I would not want to schlepp around the MK390 for stalking purposes, but it is fine for shooting from a stationary position (such as hunting stand) and even better if you can rest the rifle for firing.
With that said, there is a way to compensate for the lack of light amplification of the MK390 compared to the Gen II scopes. Get a better illuminator.
I have tried IR LED flashlight illuminators that run on 2 CR123 batteries. They will get you out to about 75 yards for darker objects and 100 or so for light colored objects. Basically, you just need an IR lamp assembly that fits a P60 type of light with a 1" tube and the new IR illuminator can be mounted on a rail (the scope ring serving as the mount). The lamp can be had for anywhere from $13-30 and some complete IR lights, such as from Solarforce for $30-40.
The Hyper Beam Red Eye (2x10) will run you about $230. Like ATN's long range illuminator, the Red Eye has a focus that will change the beam from flood to spot. This isn't a great light for the money, though it will get you out beyond 125 yards with a Gen II scope and 100 or so with Gen I. I don't think it is worth the money.
The most outstanding illuminator that I have found is the Luna Optics ELIR-2. It is a laser illuminator with a beam that can be changed from flood to laser pointer. You like want the ELIR-2 because it is the screw mount model. They are actually made to fit on Luna Optics NV scopes, but Jager Pro has an adapter that will accept the ELIR-2 that will screw onto the adapter that than then be mounted on a rail. The cheapest I have found the ELIR-2 is for $350 and the Jager Pro mount is about $30.
Jager Pro reports being able to see out to 800 yards with Gen III scopes using the ELIR-2. That may be true. What I can tell you is that the ELIR-2 when used with the MK390 that you can see very well out to 250 yards and I know that it works fine for light objects out beyond 300 yards.
So instead of spending $1500 for a higher gen scope, I would suggest buying the MK390 for $500 and then get the ELIR-2 and the mount for about $880 combined.
The MK390 can be had for $500 (shipping included) from Optics Planet, though if you look around you can find other vendors with the same deal.
You can get the ELIR-2 (which is the
SCREW mount) from here...
http://www.nightvisionetc.com/58-luna-optics-elir-laser-infrared-illuminator.html
The adapter mount can be had through Jager Pro here...
http://www.jagerpro.com/JPStore/products.aspx?subCatID=104&catID=101&typeID=
FYI, most NV scopes seem to be rated for no more than a .308, the recoil potentially damaging the electronics. This has been with case with 4 different companies I have checked including ATN. Some people have and do use NV scopes are larger calibers, but that likely isn't what the manufacturers are suggesting.
