And to add to what RCKen and several of us have said, I like them, and most beginners find them easy to use and set up very quickly.  You either see your success or failure right away!   Then, if satisfied, move on.. if not, remove them (cut them with a razor or Xacto knife), shift the hinge point an inch or so and do it again.  Easy and simple, and a good learning tool.

CGr.