The sill brush won't last long at all, I have had one on 3 weeks and it is looking very well used already with several lots of bristles missing.
I have commented on this before, apparently the general consensus is my technique (although no one has seen it??), this will most probably be the last gardiners sill brush I have, it is the third one that has pretty much fallen to pieces.
They are a good brush, but are just too fragile for the amount of work I expect them to do.
I am going to try the new Unger Ntech brush, slightly larger and heavier, but am hoping more robusttoo.