I accepted one of these, and after I was able to access the guidelines, I immediately cancelled.
Way, way too much work (and, yes, if you do not use the phrase they want word for word, your shop will be rejected) for the tiny, tiny fee. You are totally out of pocket until the refund arrives; you're out of pocket significantly more than the shop fee. If you search the forum, you'll find many stories of shoppers unable to get "on the spot" refunds (for the scenarios that actually require sending money). And even more stories of shops rejected due to the shopper either not using the exact, word for word phrase, and so on.
On my 10 foot pole list.