Love seeing fellow fountian pen collectors on here! :clap:
I have 12 or 13 FP's myself, nothing too expensive, mostly Lamys & Kawecos, but planning to add a Waterman, Twsbi, and Mont Blanc to my collection in a few months. And I don't care for ink cartridges, it's either vacuum converters or eyedropper conversions all the way! That way you are free to use every amazing color and brand of FP, ink you wish!
(Check out gouletpens.com (no affiliation, but love their selection)
To me, using a cartridge is like smoking a ciggarette, both are pre-filled with a limited selection of product and disposable. But a converter...that's like a good cob or briar, fill it with whatever your current favorite may be, and enjoy again and again!