I figured out (might be a bug) that DURING flight with the Darktrooper, you can re-charge your caster (not having it charged before flight, but during the flight you can). Use it to your advantage. You can have a 2/3 charged clip when you land if timed right, and can take out 2 enemies that have been in a firefight.
With Jet Trooper, when i see a group of 5-ish enemies, i fly up and toward them, then (while in air) fire off an EMP round (might want to lead the target a bit) at the biggest clump of them. Then you land, run in circles, roll, and do whatever it takes to stay alive long enough to get back in the air, repeat, and try again. when your down to 1 enemy, just finish him off with the pistol.
Both worked great for me