Is it better for a current Xfinity Mobile customer to buy a new iphone from Apple or from Xfinity?

The price is the same, and if you buy it from Apple you can get it put on your Xfinity Mobile account with the same number. The only difference seems to be that Xfinity Mobile will send you a $250 gift card if you buy it from them. Is there a catch somewhere? Are the phones going to be different somehow?