Tyler Cowen is skeptical of them:
I'm not sure if these places will still be going in three years' time. Part of the problem is if you're a customer and what you pay is voluntary, you're under pressure to pay a lot of money. You do it once to prove to yourself and others how charitable you are, but how many people go back 17 times? I would find it a burden -- my reputation is on the line. What if I only pay $ 27 instead of $ 34? What does my date think? What does my wife think? You end up wanting to feel liberated and just paying a listed cash price. I think there's no way to solve that problem.