I recently bought an Armalite M-15A4 carbine, and topped it with an EOtech 512.  The performance so far has been very nice - accurage and no malfunctions.

Yesterday I tried shooting from inside my barn (quite dark) to a target in bright sunlight about 50 yards away.  The target was a standard NRA pistol target, with an aiming black of about 2.5".  What  surprised me was that at the medium "turn on" setting, the reticle totally washed out.  I had to run it up to the brightest setting to see the center reticle dot against the black, and even then it was marginal.  The reticle actually showed up better against the buff-colored paper.  

Anyhow, the lesson for me, as has been said on this forum plenty of times, is that training must include all conditions.