The condom method generally leads to uneven or incomplete filling and if you soak the inner tube too much, it will expand and choke off the air tube.
I've done a lot of fill testing with various methods and clear cartomizers to see how the fill progresses. While I'm not necessarily a fan of the end cap fill method, done properly I've yet to see a fill that I would call uneven or incomplete compared to any other method. I'd say that it's better to fill this way from the battery end rather than the mouthpiece, but beyond that it's mostly just a matter of not rushing the process or quitting before it's finished (which can admittedly be hard to tell with standard cartos). A Taryn spin in between cap/fill cycles does help a lot. In testing with clear cartomizers it only takes about 2 seconds of spin to pull most of the liquid toward the bottom.
I've never seen a tube
expand in a way that I would associate to a given or specific fill method. I have seen a few cartos with tubes that seemed expanded or collapsed but they had been refilled several times with a variety of methods. I think they were really cheap 510's which I simply don't buy anymore.
But that tube in the center is the weak point in just about any fill method other than dripping or syringe filling. It's a "path of least resistance" and diverts nicquid to the top or bottom rather than the fill material. That's not insurmountable but it is inconvenient.
Some try blocking the tube with a Q-Tip stick or something similar, but in testing I've managed to damage vertical
coils and horizontal
coils/wicks and/or the tube itself that way.
A couple of fill methods I've played with benefit from either flushing nicquid through the entire carto 2 to 3 times or temporarily blocking the top of the cartomizer so pressure directs nicquid out to the fill rather than directly to the top of the tube.
All of that said, I must say that the drip method tests out
very well for consistently and completely filling a cartomizer (it's actually kind of fun to watch with a clear cartomizer). The only real drawback is that it's time consuming (for bigger cartomizers) or at least
feels that way (for smaller ones).
I would love, love LOVE to see or come up with an inexpensive, thorough and
automated way of cleaning and filling cartos. With some of the newer, better cartomizer systems that are out now, the time it takes to clean and refill cartos is just about the biggest obstacle left that most new vapers will face.