It doesn't sound any different than a typical on line TA. they pretty much all offer some on-board credit & all run the "specials" from time to time- all without a membership fee. I get leery of any business that requires me to be a member in order to get their "special" prices.
I suppose if I could get a price before
joining & it were to be much better than any TA that I deal with I might reconsider.