There were a couple production runs that had problems going through batteries. I've not heard this to be a problem for a while now.
I've got a 512 going on eight years now with zero problems. Stays zeroed, have kept same batteries in it for months and turns right on, bright and good to go ... And frankly, given the cheap price of replacement batteries, I could care less if I have to occasionally replace batteries. Yeah, it's great that my AIMPOINT can stay turned on for three years, but gosh, are you guys too cheap and too lazy to swap out double-As?
The controls stink? Huh? Yeah, they're a little small and hard to get to if your device is snugged back toward your BUIS, and you need two thumbs to turn it off, but really, they're not that bad ...
If you don't require a HWS compatible with night-vision devices, the 512 is one of the best. I'll always have a 512 mounted on one of my M-4s.
And um, OpticsPlanet, you can get an absolute co-witness with a 512, don't need the XPS2 (a worthy HWS for sure) for that ...
If you need further affirmation that your 512 is GTG, go over to ARFCOM, lots of fans there (lots of AIMPOINT and ACOG fanboys, too) ...