Pigeon -
I have 2 511 models and love them.........buuuuuutttt I am an anal retentive geek who constantly "checks s**t". I have no trouble in my area finding the N cells
(they are 1.5v and are strikingly similar to a different voltage battery cell that will blow your Eotech 3 feet off the rail and take your fire control hand with it!!!!!) OKAY, I made that last part up but the wrong battery will fry them, you must make sure they are the N CELLs if you go with the 511. These batteries can sometimes be found in drugstores and pharmacies under the "medical" supply section. I like the small front end on these models and have no trouble turning them off and on when I go train. I have not had any issues with battery terminal corrosion or case leakage, but they are not too terribly abused. I have an aimpoint comp M2 on my primary AR and beat the hell out of it and never turn it off.
I would buy the 511 model again if in the same situation I was before. (Not loving the Aimpoint so much).
Let us know what you decide to go with!
"We would never invade the United States. That would be foolish. Behind every blade of grass there is a rifle." Admiral Isoroku Yamamoto