Gen 2 has a smaller profile than Gen1 to fit better underneath a mounted scope. The front MBUS also has something else to do with the way the front post sits in the sight. I prefer the Gen2
I have Gen 1 MBUS on my 15-22. I run a Vortex Strikefire and have no issues with the larger profile. Besides I got them front and rear for $35 shipped LNIB.
I looked at both and bought the Gen2 because of the lower profile which IMHO just plain looks obtrusive folded down which mine are 99 percent of the time.