A&K SR25 seems to be pretty good while being cheaper than cyma nowadays. I just couldn't remember whether it has a full cylinder or not.
I can't say much lest I gave wrong information since that topic is still beyond my understanding. But the basic is that since the compression area lays a few while after the piston moves, it gave the piston faster speed before it starts compressing air for real, giving us higher pressure spike. It supposedly helps us gain range in limited power build.Not exactly sure what advantage that you are talking about, I know of some though.
Please clarify your point.