I have one. It helps on the complex angles, but you really need 3 hands when using it. A hand to hold the pipe, one to hold the jig, and a third to mark the cut pattern.
I never use mine. They spread out on the tube instead of conforming to it. Got them from the g/f for christmas so i dont feel too bad about it but its def. not worth the cash. Use them only on REALLY crazy notches and then i just conform it myself and make it fit the angle.