I've got 2 fdm printers, older versions so probably not as user friendly as newer ones, or more expensive ones. I tried making a business out of it for a few years. I've heard the prussia is the gold standard with that style, most user firendly, etc. but it's a couple of grand. Mine were a couple hundred bucks. If you've done any fab work or machining, it opens up some new shapes and methods, but if you don't have any 3d modeling experience (or a desire/time to learn) then you won't get much practical use out of it.
The basic plastics that are easy to print don't hold up, the ones that hold up somewhat better are much harder to get a good print (but that could just be my cheaper diy printers, vs the couple grand Prussia). None of them hold up all that well, at least there materials I've used. Great for around the house things, not so much for tractor parts that are exposed to sun and vibration. I have yet to try using one for a mold to cast parts with though, but that's at the top of my eventually list.
Slicing software is also a big deal, that turns your model into printer code, and a good one takes good paths and generate supports in good spots, but a bad one might be functional but just make everything take twice as long, worse supports making sagging, not great layers, etc. Depends on what you're looking to do with it, but if everything is tight, the slicing software is going to be where your learning curve and success is, the hardware is just speed and size.
Disclaimer: it's been about 3 years since I messed with this stuff, so the above information could be outdated.