I use a 17' xtel, great closed length and light but a bit bendy, I think it would be pretty impossible with the weight of a sill brush. Also have a 28' xtel hybrid, that is a really good pole very rigid and still a pretty good closed length.
If your not looking to buy one until the end of Jan I would give the slx from Gardeners a bit of thought. About as light as my 17'xtel and more rigid than anything.
Simon.