I've used them intermittently for years, but primarily the very cheap ones, and modern ones tend not to need a huge amount of maintenance if you're using them at least semi-regularly. But last year I fell down the rabbit hole when I decided to see if I could replace my Parker Vector calligraphy set and Amazon's Mighty Algorithm took that as the cue to wave cheap Chinese fountain pens at me.

They do have a serious use for me, because my RSI means that a pen that doesn't need any pressure is a lot more comfortable to use, and a fountain pen with a reasonable nib fits the bill. I hadn't done much writing at home for a long time, but then I got chronic migrraine and staying away from the computer was a really good idea, so composing first and transcribing later was useful.