My advice is get a vikan sill ................
Why would you advise this? The Vikan sill brush is a specialist brush, it very heavy and unless you need a specific requirement to scrub sills and need bristles everywhere its frankly overkill. And as the OP has said he intends on using a CLX pole which is a lightweight pole it will make his pole bend and flex uneccesarily and he won't get the benefit of either. Anyone can scrub sills with a standard brush, just 'angle it'.
and a red aeriel brush nobody likes the vikan because it makes there arms hurt 
I've strong arms so I find it a great brush and the superlite poope as it just bounces off the glass and scratches sills and frames.
Aeriel is amazing brush.much quicker to use than the rest and cleans glass really well as it does sills and frames.
The ariel brush certainley seems like a fine brush, you don't like the superlite in its various trims, filaments? Whatever, they're all subject to their fans or detesters. But one thing is for sure, he needs a lightweight brush on the end of a CLX and Vikan don't make any that i'm aware of. You can have the strongest arms in the world and they won't stop a lightweight composite pole being 'whippy' with a heavy brush on the end.