It should work either way unless the board is a lot taller than the fence. If you try and go handheld, you will probably have to keep moving clamps around out of the way. I don't normally worry about feather boards when rounding edges off as the only way the board can go is away from the bit, and fence if on a table. You can do it on a table without a fence with a bearing guided bit which is probably what you have. I do usually make a second pass just in case I didn't get it smooth on the 1st. Rounding over, especially with a bearing guided bit, is one of the most foolproof operations you can do with a router.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.