To me at least that's an _extremely_ rude thing to do. (Unless one person is asked to do it this way, the other one that way, so people can compare the outcome.

To me at least that's an _extremely_ rude thing to do. (Unless one person is asked to do it this way, the other one that way, so people can compare the outcome.) (Especially if they aren't made aware of each other until the end.)