I've got both the yellow WCW backpack (£100 ish) and the Shurflo Backpack (£300 ish), and the Shurflo is more suitable for someone whose going to use it as their primary means of cleaning windows. My shurflo is four years old and has had a right hammering. Some days I've put 200 litres through there; which is a lot for a backpack.
Contrast that with the WCW backpack, I've hardly used it and it's falling to bits already!
The WCW backpack is more suitable for a compliment to a van-mount system where it's only used occasionally, and not day-in-day-out.
I can't answer the rest of the questions; gotta go!
