Well, there's always something fishy in this FEE-less, no limits promotions. I don't know what to say about this they have to profit from it in a way or another.
Another good project for exchanging is bankera, they got fees though as any other bank do, but they're needed in order to sustain them in the beginning at least ;)
They collect interest off of the coins held in your wallet I believe. I am not sure the exact numbers as I haven't used it yet, but I did read something about that. Plus they offer a premium service geered towards traders that is a paid service. So yes, they make up for it in different ways.