I bought one of these last week. I am not over impressed with it. But for the price I guess I should not expect too much.
The biggest issue I have is the flow rate.
It has a three position switch. Low, Off, Full. and a dial for fine adjustment, But on Low and with the dial turned right down the water comes out so hard it bounces off the windows. that makes the rest of the settings useless.
I want it for working inside a building leaning out to reach the outside as this is the only way to access certain windows. With the water flowing as fast as it does I will empty a tank in no time. So I expect I am going to be making dozens of journeys back to the van to re fill.

I contacted Gardiners and got the reply... "Unfortunately if it is set to 1 then this would be the lowest setting. The backpacks do need to pump at a certain amount of pressure in order to pump the water up the pole sufficiently."
Whilst I agree to a point with this reply I would ask why was it only designed for working at height? Would it not have made sense to consider the fact ground floor and low level windows need cleaning too?