Don't get an UNGER pole get the "CLEANTECH" pole. It's an aluminium screw clamped pole same as the Unger but the screw clamps are bigger, better and easier to use. You can easily replace the inner clamps when they wear out.
I have an 18' CEANTECH pole I use most of the time and a 30' UNGER telepole.
To be honest, using the Unger is awkward as I have to struggle with the cones when extending it - even after replaceing the clamps!
David