The FMA can keep the heli level by controlling the pitch and roll axis. I'm not positive but I think it uses infrared sensors to detect the ground versus air and levels accordingly.
I can see there are times I could have used one. Sometime I get out too far to see what the heli is really doing. If I could flip a switch and it would level the heli till I could get my bearings that would be worth the money. Down fall is it probably won't work on a CCPM machine as it couldn't control the pitch servo.
Later,,,basmntdweller