A few shots of mine....
I am running an EOTech 552 Holosight with an EOTech 3x magnifier. Since I utilize an ARMS S.I.R. #50M rail, my BUIS will not cowitness with the 552 unless I use the bilevel rail at the front end of the 50M. To get around this, I employ a GG&G Accucam QD mount on the 552, so in the event of it failing, I can quickly remove the 552, flip the magnifier out of the way (it has a flip-to-the-side mount), deploy the BUIS, and I'm back in business.
The Holosights (unmagnified) are designed to be used with both eyes open. Once the reticle is zeroed, it will remain true to aim regardless of where the shooter positions his/her head in relation to the optic. The reticle will superimpose in the shooter's field of vision making HUD type effect and allowing for a wider range of vision. (Mine does not have the BDC reticle, althought the newer 557's do). The reticle is a 1 moa dot surrounded by a 65 moa circle.
Once the holosight is zeroed, flip the mag in place and center the reticle in the field of view with the adjustment screws on the mag base. Then flip it out of the way and flip it back. You will have to repeat this a couple of times before you get it where you want it and it stays there. After that, no problems. It stays there. You don't have to re-zero it to use the mag. It retains the zero from the non-magnified aspect as is consistant with a holosight. The magnifier does enlarge the reticle, but it is appropriate with the sight picture. It also clarifies the reticle making it much sharper. It really does improve your potential accuracy. There is no adjustment for the shooter when changing from magnified to non-magnified. It's really nice that way. It still has a good field of view under magnification as it is just like looking through a 3x scope ('cause it is). And that is exactly what it is like, looking through a 3x power scope with an electronic reticle. The picture is very clear and sharp on the magnifiers (for those concerned about the quality of the glass). The unit itself is beefier and much more sturdy than I imagined. And a little bigger than I had expected, which was good for me as some of the pictures make it look small.
In order for all of the site systems on my rifle to work together, I did have to move my 552 forward a couple of rungs, so I had to re-zero it at the range. (Which still seemed to hit dead on even after I moved it). With my current configuration, I have the mag base almost up against the buis (ARMS 40) and the 552 all but touching the mag. I can get my thick fingers in between the two to operate the controls on the 552, but it is not the smoothest operation in the world. Flipping the mag out of the way makes this a little easier, but it is not a problem for me. This may not be acceptable to some shooters, so they may want to space the distance between the components out a little bit. With the mag flipped out of the way, the BUIS deploys just fine. (I don't currently have a QD setup for removing the 552 as I am using the large thumbscrew, but I plan on getting one). The shooter loses very little (if any) peripheral sight with the mag flipped out of the way.
Having said all that, this setup is probably not for everyone. This setup is nice for the shooter that wants the ability to switch from a quick acquisition battle site to a magnified battle site quickly without having to switch (remove/attach) hardware. It does that very well. Price wise, it is around $500 for the 3x with the flip to the side mount. The 4x is almost $700, which seems like a huge difference in price for only 1x more power. That is in addition to the holosight, which can run anywhere from $300 - $500 depending on your choice there. They are supposed to line up with all of the current EOTech holosights, and mine was no different. It lined up upon mounting it, with only a couple of adjustments needed to get it where I wanted it (after flipping it several times, it stayed where I wanted it throughout the range session, and was more accurate than I was). The setup can be pricey, but not in comparison with some of the higher end ACOG's. They (EOTech) offer the magnifiers with a stationary mount also (one that doesn't flip), but that defeats the purpose for this type of setup, ie. having 2 components to achieve magnified view so as to be able to switch between the 2 depending on the needs of a particular situation. The ACOG would probably be a better choice if you were not going to switch between magnified and unmagnified, opting for magnified all the time. The EOTech flip to the side setup is to facilitate switching between the 2 options without having to switch hardware. Again, it does this well.
I love mine, and I highly recommend this setup to anyone considering one. They are badass!! I thought that I would spend all day running on magnification, but I found myself switching between the 2 constantly, and having a blast doing it. (Maybe it's just something about being able to do it that makes it fun). Hard to describe, you kinda have to experience it. In my opinion, this is not a gimmick. It is an innovation that really works and is highly effective (realizing that Aimpoint was doing this prior, so credit for the idea goes elsewhere). Point being is that the setup works well. If you have any questions regarding this, please feel free to post it or PM me (be advised that I am NOT military or LEO and have not used this setup in either of those venues). I will answer what I can.