If you don't have the money to buy a bulk lot of shirts and sell them yourself this is a good service for you. We have a small, but dedicated listener base and they wanted swag, we couldn't afford to stock it, so TeeSpring helped with that. Just stay with the Hanes products, the "premium" stuff falls short of expectation. Pay attention to the tips they give for constantly available items, as failing to set it up just right might leave your customers waiting a month for their products.
You have to learn the ropes a little, but it has made a few bucks to help us keep doing what we enjoy doing, and our listeners are pretty happy to have a shirt to support the show.