You don't need the accessories or expensive cleaning fluids...,
This review is from: Kärcher WV50 Window Vac - Window Cleaning Vacuum (DIY & Tools)
I just got the vac, none of the extra accessories and had noticed our window cleaners just use washing up liquid to great effect.
So armed with an old spray bottle left over from a cleaning product filled with some warm water and a little fairy I sprayed the windows, wiped them with down with a cloth and then used the vac.
I was initially skeptical, especially as I hadn't realised it was just a vac. I had expected some kind of steamer. But in just under the 20 minutes battery life I'd done what I needed and the improvements were dramatic.
We have large patio windows across the back of the house probably about 50 metres square of glass if you count both sides and they are always in a state thanks to 2 small kids and 3 dogs now they looked great.
Was it perfect? No, but it was pretty close. Our window cleaner rarely left them perfect either and it was also my first go.
It's better if you can do a swipe down the window in one go and don't stop mid way and on the inside it was hard to get all the way to the bottom of our window as the glass goes practically to the floor (so had to swipe up to do that).
We'd tried lots of glass cleaning sprays and fluids in the past with an assortment of cloth types but were always left with varying degrees of streaky mess. So it was surprising what a little washing up liquid did instead.
Obviously you could do the same for less with similar tools to those window cleaners use. These would cost less, but there is more effort required and more excess liquid to deal with so needs a little more skill and a potentially had a wetter inside!
The price does seem high for what it is, but for us it will quickly pay for itself. No more Mr Muscle spray or waiting for the window cleaners to turn up (and then we're never in for them to do the back or to do inside). They can keep doing the front it was the large expanse at the back we'd like to be able to see out/not be embarrassed about that matters and we know we can do it quickly when needed.
Battery could be an issue. 20 minutes isn't long. I actually ran out on the last side (8 large sides) but that was because I redid a window my wife did as she is too short to reach very high! I do think I would be quicker next time but we do have a lot of glass and no way you could do inside and out of an average home in one charge. If it is an issue you have to question if you need to do the whole house in one go and how often you need to do it. Most of our windows can go for ages without a wash so for our needs 20 minutes is fine.