Are consumer level 3D printers able to print plastic objects of similar quality to ones produced using injection molding? Or is 3D printing useful mostly for the prototyping stage before a design is finalized and a steel mold is produced for injection molding?
Generally speaking - there aren’t many areas where the finished product using 3d printing is better than more traditional methods. The main advantage of 3d printing is the flexibility. Injection molding will pretty much always give you a better result, but you’ll be able to go from idea to physical prototype much more quickly with 3d printing - not to mention that your average person isn’t going to be able/willing to set up an injection mold in their homes.
In industrial use (so not consumers) the main use for 3d printing is indeed rapid prototyping, 3d printing doesn’t really scale all that well to mass production, but if you’re going to be iterating on a design several times before getting something you’re comfortable with, then it’s a great choice
Sig Sauer and Walker Defense have both done some very cool things with mass-produced printed metal. Sig is, for instance, making silencers for their Spear rifles (at least the ones chambered in .277 Fury/6.8 x 51mm) that can’t be done with traditional subtractive machining. Walker Defense makes a very unusual compensator that also couldn’t be made with traditional machining; neither of those could readily be made through molding either. It’s not cheap, but they’re still mass-produced items. The surface finish isn’t perfect, but it’s pretty damn good.
These are both currently beyond the capabilities of home printers, since people don’t generally have the ovens needed to sinter Inconel parts.
Using it for jewelry is pretty good. Better than the injection process