Just bought the M4 last week. I fired it over the weekend and I loved it. I don't have much experience with red dots other than my Tasco I about at Wallyworld.

What I liked.
-2 MOA
- Uses AA batteries
-Can cowitness without buying any sort of riser

It is much bigger and a bit heavier than I expected. This doesn't bother me. I actually like giving the 15-22 a bit more weight.

If size and weight is a factor then go with the Micro.

If you mostly plan on shooting short distances say 25 yards, then you may want to look at the reflex red dot.