3D printing has its niches where it works well and is profitable.
For example for low volumes of small products it will be cheaper than investing in an injection mold.
Plus you can manufacture on-demand and customize the end product. The quality can be quite good though it will not come very near to IM quality.
So taking all pros and cons into account you need at least some sort of business plan, and early tests for proof of concept.
It is all about your idea and how you present yourself.
I haven't seen anything promising coming out of 3D printer pens, to me it's more like a nifty toy.
So I would go for an entry-level 3D printer.