The key is to ensure not just the root, but the entire root sheath (clear jelly sock) surrounding the lower part of the hair, is completely removed along with the root itself. The cells located in the middle of the root sheath are the germinative cells that stimulate hair regrowth. Hair growth is not caused by the cells located at the base of the root. So just because a hair is removed intact with the root attached, doesn't mean it will not regrow. You want to make sure you inspect the epillated hairs to see both the root, and the clear root sheath wrapped around the lower third, completely unbroken. This is the best way to make sure it won't grow back.
If performed properly, pain should be little. Especially with the Apilus.