At the Window cleaning Warehouse I saw a new Vikan brush that had mono filament bristles
....at least I think it was Vikan
For me the best I've come across in use so far is the Bentley brush.
Exceptionally light, good bristle length, retains its shape and has good splay in use.
Bentley had a stand at the show, to be honest, I didn't see a brush there that I thought would be suitable...they were all far too heavy for my liking.
The white one is top banana though
Ian