Those tend to have extremely limited usefulness. Good enough to assassinate a single person at point blank range before they catastrophically fail but (unless something has changed) not much else. Plastic just isn't cut out for the job.

You still need metal parts, notably a gun barrel capable of holding extreme pressures until the bullet gets up to speed. That isn’t plastic. The grip and frame might be plastic, but not the barrel.

Don't you still need metal bullets for the 3d printed gun?

You are better off using a lathe to make a gun.