I've used it quite a bit. Really don't need to put anything else over it, though I have occasionally dipped them in Bohning lacquer for added weight. Bopnded OK, but shooting into targets would rub off the lacquer. I expect the same thing would happen with poly. If you do choose to do it, make sure the watco is completely dry, i.e., let it dry a week or more before coating it with something else.
Again, if you hand rub multiple coats, or better yet, soak the arrows in the oil for several days, it provides a good finish all by itself when dry.