Been very happy with Burris fastfire for a number of years on multiple guns. Switched out 2s for 3s when the 3 came out for ease of battery replacement (though a battery lasts a long time)
I just bought a new M2 and will use the Fastfire 3 and a speed bead mount. Currently I use the weaver rail and that works fine. As others have said the Sumtoy or Burris 336 mount will get it lower than the rail but not as low as the speed bead
