Bit late but we have used it quite a bit. They have a few different ones with varying levels of quality. Their main merchant API which returns a list of all their merchants in X category is rubbish. It is both very out of date and too update at the same time, in that they don't delete old, merchants very often and often add new ones before they are live on the network.
The product search API seams much better we have been using it a bit a it seams more reliable than the merchant which some just didn't reply, but it also suffers from things out of date.
We are just starting to look at their full product feeds but are more hopeful for them as they more often done 3rd parties and the merchants themselves.