So, this is probably more than you want to know, but if you're interested in fountain pens, I can't recommend highly enough the Goulet pens info vids. They'll tell you a lot about today's fountain pens, and currently available inks.
I started with Sheaffer's school pens and cartridges (click through pictures), progressed to Sheaffer No Nonsense pens. At the time, I was unaware of converter fillers, but I cajoled a used, needle-less syringe from my cat's vet, and used it to refill cartridges with bottled ink, eliminating throwaway cartridges and spending money on new ones. Adults used lever-fill fountain pens, and when I first started collecting vintage fountain pens, they were what I thought of as "real pens." Here's a YouTube link on a series of care and feeding vids for lever-fill pens. https://www.youtube.com/results?search_query=cleaning+and+filling+lever-fill+fountain+pen You can find lever fill, and vintage pens with other types of fillers at flea markets, yard sales and, of course, on ebay for very little money. Sometimes they might need a little repair or refurbishing, but even adding in those costs, a vintage pen can serve you well for very little money. Most of my pens have been acquired this way, other than my dad's lever-fill Sheaffer, my mom's Parker Vacuumatic, and my husband's piston-fill Pelikan.
When my husband bought me my first "real" fountain pen, a Parker 45, it came with both cartridges and converter, and I never used cartridges again. I discovered twist-piston filling converters, and have always subbed them for the pinch-type converters which a lot of pens came with, because you can see the ink level in them, unlike the metal-housed pinch fill ones.
Today's fountain pens almost all come with twist-fill piston converters, and I've replaced cartridges and pinch-converters in every pen that will accept a converter. My Sheaffer Connaisseur, released by Levenger as the "Mediterranean" of its "Seas" series, has a solid block at the end of the barrel to improve the pen's balance. But it also shortens the available space and makes a twist converter unusable. The rest of my pinch converters have been replaced.
As I said, more than you wanted to know, I'm sure. But maybe you'll find some of the links interesting, or helpful, if you decide to fall willy-nilly into the wonderful world of fountain pens.