Hi, and thanks for your replies!
But I didn't understand what you meant with that it can be unstable due to people registering then abusing the service until their account gets suspended? How would I be abusing it?
I want to open a web shop with PayPal-buttons (Add to cart) where I sell music DVDs imported from around the world (legit DVDs, not illegal pirate copies). Am I allowed to do this on your free service?