I think I would like to see the Max 11/15 and Max 11a1/15 side by side to know for sure, but I think I prefer the looks of the Max 11/15? Just my opinion.
Mechanically, the AR recoil mechanism is the same as the MAX-11/15 except the operating rod is shorter by 2”. Same stroke length. The IRM is significantly different. Had to get real creative to get it to fit and keep the mass up.