I think what's a game-changer here is if they only charge your credit card after the 7 days. It's not very clear, but they do say that you only pay for what you keep. And this could be huge.

15 items could easily be $1,000, and asking someone to pay a $1,000 just to try, even if they know they can return and get a refund, is a huge barrier. If Amazon would indeed charge you only after the 7-days, they could convert a lot of store buyers their ways.