I have both the Eotech 511 and the Aimpoint Comp M. While I like both, I feel that the Eotech is basically more advanced - at least from a user perspective if not a technical perspective. While the Eotech is a bigger, this also allows for a greater FOV - I don't really even notice the housing of the Eotech as I do the tube on the aimpoint. From a total cost perspective on a flattop AR, the Eotech is also almost always going to win, as you don't need to purchase a separate mount for it. The battery life issue was addressed in revision F, but I believe these are in short supply right now, which probably won't change anytime soon. Eotech was just awarded a large contract for the SOPMOD2 project (along with Eclan and Trijicon) so most new production will likely be focused on that. Interestingly, Aimpoint, was NOT awarded part of that contract - reinforcing my idea that while both are good, the Eotech is the "new" while Aimpoint the "old".
Rocko