I’ve only tried one fountain pen. It was a kit from Rockler (I think). Not much different to make and turn than any other pen style, but the nib that came with it was horrible. I later found out that most who make fountain pens to sell or as a special gift that will actually be used, go through companies which specialize in fountain pens. Where the kit from Rockler is about $10 (or used to be), just the nib for a good one is $20 or more and I remember seeing kits that were in the $40 range for just the internals. I don’t remembered any of the company names, but a quick search should turn up a few.
I did try to break in the Rockler nib, but the lines were always blotchy and I was always scratching the paper.
I did see a few kits that allowed a variety of ink delivery systems (siphon, cartridge and bulb), but they were from companies that appeared to only sell fountain pens. When I start back again, I’ll go with a better quality kit, but it’s going to be a gift.
As a side note, there are instructions that let you make the threaded sections from the wood or acrylic pieces, but that skill is so far above me that I’ll stick with the kits that have the metal threaded pieces.