It's annoying because Lamy has its own cartridge shape, so even if you have the pens you still need the carts, or if the converter breaks (which they do) you need to get one from them. I know Monteverde also makes Lamy shaped carts, but again, because Lamy is everywhere it's easier to just grab Lamy carts than order Monteverde. I dunno, it sucks.

I like Pilot and one of my favorite pens is a Pilot, but both Pilots and Platinums have their own cartridge shape as well.