We’ve got one – brilliant product. Far better cleaning than the ‘professional window cleaners who did that touchless washing with fancy water through a long lance from ground level (which was crap).
what do you mean when you say “cleaning windows”? It’s basically a squeegee with a vacuum, right? So do you mean you use it to clean off the soapy water (or whatever) you use to clean the windows?
I use mine similar to that: more to remove the soapy water from the glass than actual cleaning. I use the Karcher cleaner stuff diluted in a spray bottle, a few squirts per window then wiped over with a sponge from a bucket of warm water (no other soap/cleaning stuff), then clear the water off with the window vac. That method works for me.
I’ve found wiping the blade with a microfibre cloth between each ‘wipe’ of the window helps it collect all water from the top edge of the window.
They’re also robust buggers. Lost grip on ours cleaning the dormer windows once. Slid down roof and fell one storey onto monoblocks. Unharmed apart from one of the tabs holding bottle in place snapped, but a bit of tape fixed that.