Considering the absurdly low payoff relative to the amount spent, I'd almost rather have the blogger say "hey, if you really want to support the blog, donate $4 to me and spend the other $671 on actual travel things and enjoy yourself." Supporting such a charlatan website, where I honestly feel most people won't see that $675 back, simply because of $4 per person referral would turn me off completely from a blog. Sure, it might be "free" for now, but the fact that they're offering, effectively, "$675 off" ought to tell you something. A Delta Sky Club individual membership is less than that!