This is the new Aimpoint CompM4, the next evolutionary step in Aimpoint's excellent M2/M3 series. It uses a single AA battery for 8 years of 24/7 use at setting 12 and has 7 NV settings and 9 day settings (w/the last being extra bright). W/E caps are better protected as is the rear-facing brightness control knob (the indicator line on the knob is a nice touch, allowing you to visually check the appx brightness setting). The integral QD mount auto-sets proper torque when installing (so no need to guess how much torque to apply) and is keyed to the optic itself to absorb recoil & impacts. It also comes w/a detachable riser so as to make it compatible w/various platforms (shown removed in these pics). An ARD killflash is part of the package as is a heavy-duty rubber bikini lens cover (which seals very well against the elements but, IMHO, is somewhat slow to attach/remove). On my PS90's it sits low enough to provide excellent cheekweld when using the dual mag setup or good chinweld when using a single mag. Typical Aimpoint quality is evident everywhere. If you already have a good M2/M3 setup (or other optic) that you're happy with then the M4 probably isn't worth upgrading to. However, if you're in the market for a new Aimpoint or an excellent CQB optic that's good to go "right out of the box" w/mount, killflash & lens cover then the M4 is worth considering.