I have for over a month now been using an Adis brush on my short pole, this is a brush that is used to go on a broom (not the wooden block type though!!), I drilled it and put in jets just as a trial, I have just fitted one onto my new pole in place of a Vikan brush and will start using it on upstairs work on Monday.
It fits straight onto your normal angle crank adapter and works a treat - all for the princely sum of 3-25 - it may look a bit short of bristles BUT it is extremely light and seems to shift bird muck easily.
You can buy them in either stiff or soft (I use soft), I used it on a conservatory roof last week as a trial and it worked very well with the bonus of it doesn't trap any dirt either.
Marc