Hi Clive
I think the 17ft should be easily manageable and sounds like a good inexpensive pole.
The problem with the Gf x-tel on the 24ft is that they are apparently very whippy and this is what I believe causes the extra strain on your back. A more rigid lightweight pole should be a big improvement especially for lifting off the windows when rinsing.
Still haven’t got my hand in my pocket and I have two busy days this week with quite a few 3 story houses.

Wayne