i have
medium bristle sill brush(white)
soft bristle sill brush(black)
medium bristle extreme brush(white)
the sill brushes are ok but i use the extreme for most normal work.
the white sill brush is the one to go for if your just buying one specifically for 2nd floor sills and velux.of course you can use it for all your maintenance cleaning if you want but i prefer the extreme because of the points ive made above.
hope this makes things clearer for you mate!!
regards
dazmond