I use a 21ft x-tel as my everyday pole and it's great.
I always try to use a bit of each section rather than just the top 2, as the pole will be much more rigid.
also I would advise that you don't use any section fully extended over coservatory roofs etc as the ends of the sections can start to crack under excess stress.
I wouldn't cut it down cos those extra 3 ft are really useful at times