A new Eotech, yes. I like the 516, personally (like rjrivero said, it takes CR123 batteries, same as most weapons lights, and you can get them in the photo section at Walmart). Battery life on the 516 isn't too bad---1000-1100 hours at a pretty bright setting, more if you turn the brightness down---and it does a lower 1/3 cowitness right out of the box. The AA models have slightly shorter battery life with AA lithiums, and much shorter with AA alkalines, but on the other hand AA's are cheap.
I really like the Eotech reticle compared to a simple dot, and the dot is as precise as an unmagnified red dot can get (it is smaller than the diffraction limit of the human eye). Sight it in at 50 yards and you are within a couple inches of the line of sight all the way out to 225+ yards, and someday if you keep an AR for defensive purposes, the bottom center of the ring provides an excellent aiming point at in-the-home distances.
I'd be leery of a used Eotech because you don't know if it's one of the earlier, less reliable issues or if it's been abused.
FWIW, the Eotech model numbers can be a bit confusing, so here's a rundown:
Eotechs come in two basic flavors: (1) those that are set up for a lower-1/3 cowitness right out of the box, and (2) those that are set up for an absolute cowitness out of the box and need an aftermarket 7mm riser to do a lower-1/3. Within each of those two categories, some models have the capability to go ultra-dim for use with night vision equipment, and some don't (with NV capability jacking up the price quite a bit).
The following models are set up for a lower-1/3 cowitness out of the box, thanks to a built-in 7mm riser: Eotech 516, 517, 553, 556, 557. As far as I know, all other models (including 512, XPS series, etc.) are set up for absolute cowitness, so if you want a lower 1/3 cowitness you'll need a 7mm riser, like a LaRue QD mount.
Battery requirements are as follows:
- 516: two CR123, 1000hr runtime at brightness 12 (longer at lower settings)
- 517: two AA, 600hr runtime at brightness 12 with alkaline, 1000hr with lithium
- 553 (similar to 516 but with NV setting and QD base): two CR123, 1100 hours runtime at brightness 12
- 556 (similar to 516 but with NV setting): two CR123, 1100 hours runtime at brightness 12
- 557 (similar to 517 but with NV setting and multi-dot reticle): two AA, 600hr runtime at brightness 12 with alkaline, 1000hr with lithium
The XPS series all run off a single CR123 battery and are set up for absolute cowitness (they need a 7mm riser to do a lower 1/3). The designations are as follows:
- XPS2-0 single dot in circle (traditional Eotech reticle), no NV setting
- XPS2-1 single dot only (no circle), no NV setting
- XPS2-2 two dots in circle, no NV setting
- XPS3-0 single dot in circle (traditional Eotech reticle), NV setting
- XPS3-1 single dot only (no circle), NV setting
- XPS3-2 two dots in circle, NV setting
FWIW, if you ever find yourself looking at Aimpoints, their model designations are a bit easier to understand. Basically, the CompM series has rubber armor and night vision settings; the CompC series is the same optic but without the armor and NV, making it much cheaper; and the Micro is a scaled-down model for light weight and small size (Micro T-1 has NV capability, Micro H-1 does not). You can get various models with 2 MOA, 3 MOA, and 4 MOA dots (I prefer as small as possible). All Aimpoints will need a riser to mount properly; LaRue Tactical makes some of the best Aimpoint mounts, but there are other players in the market as well.
