Originally Posted by Shooting Addict
SRC isn't TM compatible (just the externals) so for what you want the M4 for it would be pointless, i think you should just stick with a G&G M4 variant because they are cheaper then either choices and you shouldn't have a problem for upgrades because they are 100% TM compatible to my knowledge although they seem to like parts made by CA the best. I've seen some nice gun's built of cansoft G&G (RITZ).
EDIT: KWA would be a good pick as well but i'm not sure it's TM compatible.
May I ask why TM compatible is important? Do you mean the possibility of upgrading G&G m4 with TM gearbox?