I have a cheaper simpler 3d pen I got for my birthday after the 3d doodler came out. It's okay, but I wouldn't use it to make miniatures, it's hard to keep a steady hand with this type of pen. I wouldn't attempt to make even the simplest miniatures with it - but maybe my hand is particularly unsteady.
The one thing it would be good at is if you had a drawn out design on paper and traced it, did that several times and then glued the pieces together. Almost like a printable, but done in multiple pieces. I haven't tried that though.