There are a few things to think about. First if you put their name on it, can they then enter the market with a competing product acting as though their app is yours. Second, is it a permanent arrangement? If you can get in a cancellation clause and aren't worried about the first their isn't much too lose. Every 30 days do the math and figure out how much revenue they are bringing to the table if it's more than 50% than you are gaining from the deal.