I use a vikan now and again but its a little bit soft. I now use this one I got from a local supplier, the bristles are to stiff for windows as their is not much give in the bristles and it struggles with the angle of the frames.
I nickname it the shredder, It as cut my time down by half on Con roofs, and its superb, heres a pic, I put it on my old extender pole, Nice light brush to boot.
Nel