I used the harris over a consevatory this week, I use Gaz swivel brush's on it, I found no problems with it.
I have also have unger poles I used for trad, but looking at both sets of clamps and the way they are made, the harris clamps will out last the unger, those tiny little clips in the unger clamps break for a past time, they go brittle and snap, the harris clamp is all meat with no little clips to snap.