I don't have M20A but i have M10A R2, since i don't have proper equipment to test the runtime, i will just give the general opinion.
I believe it use same circuit and same head, the only different between this two light is battery configuration and length. Basically both runs on same voltage ( 2XAA=3volt | 1xCR123=3volt).
It have very low mode if you really care about that. It's relatively well built flashlight, the selector ring also has good feeling and "click". The M10R tail cap is fully round, the switch it recessed and sometimes i feel bit tricking to activate the light. But tail cap design on M20A is different than M10R, it has kind of open channel design and i believe switch activation on M20A is much easier than switch on M10R. I also find the clip is not provide enough grip against my pocket, it would expecting the clip would give more grip.
Beam has bright hot spot and useful side spill. I just did beam shot few days ago, taken inside my boarding house, distance between flashlight and wall approx +/- 10 meters.
Low mode
High Mode
if you need more technical data, you might want check
selfbuilt review for M10R. Other review you might consider by
StickThatClucth. I will do also beam shot VS Fenix LD20 R4 ( Brighter than R2 but less throw than M10R R2 ).
