Big new article from Brian Gray on the Edison Pen Co. site:
Most of what he's written squares well with my own experience, having used many different kinds of fillers. I've gradually concluded that all filling methods have their pluses and minuses, and the Magical Wonder Filler has never yet been invented. (The syringe filler in the Gate City Belmont comes pretty close, though!) Although converters don't excite me, I understand the practical and economic reasons why they are so prevalent, and I've come to terms with them.
Unlike Brian Gray, I have had lots of problems with converters! I'm sure he only deals with high quality Schmidt K5 converters on a daily basis, so he can be forgiven for not fully appreciating how many cheap, shoddy, leaky, poorly-fitting converters are out there in the world. I've found the converters that go into better pens from major pen makers are generally good, and so is the K5. The cheaper Schmidt converters, or Lamy Safari, to say nothing of Chinese ones, are less dependable.
I feel that all converters are semi-disposable items. They are a bit dainty, and even if you get a good one to start with, you can expect it to wear out eventually. The good news is that changing them out is quick and easy. So. . . Troublesome but easy-to-fix is not a bad tradeoff.
Another problem he neglects to mention is air lock. Sometimes, especially with some dry inks, a converter will get an air bubble lodged in a way that prevents ink from flowing to the feed. It doesn't happen too often, but it can be quite a nuisance when it does. (In my experience, vac-filler pens are even more prone to this problem.)
Because of their relatively small capacity, and because they are insulated from the pen's barrel with an air space, converter pens deliver very consistent ink flow most of the time. This makes it easier to design a feed, since it doesn't have to deal with irregular surges of ink. The problem there, as Brian noted, is that those readily available feeds designed for C/C pens may prove inadequate when adapted to another filler type. Everything is connected.