My wife has one of these and thinks they are the bees knees. She does the windows, patio table, shower screens and mirrors. Streak free and lovely. The trick is not to clean the glass when it is warm/hot as the cleaner will evaporate before you get a chance to vac up. She doesn't use a water bottle but a Karcher 'mitten' attached to a dispenser which came with the vac. - darylhewston
I bought one a while ago and I followed the instructions and initially wasn't very impressed. They said to just use a spray bottle with a cloth, then use the window vac. But just using just the spray bottle didn't seem anywhere near enough water to clean the windows (which were pretty dirty) and because it was hot the windows were drying instantly and were all streaky even after using the window vac.
I had a lot more success once I used a lot more water to clean the windows. After vacuuming it still wasn't totally streak free but I was pretty happy with the results and it certainly was quick and easy. I also had a go in the bathroom and it was fantastic on the shower screen and mirror.
I think it would be really good for a glass pool fence. I've heard people say they regret getting glass fencing because it is so hard to keep clean.
I didn't use the battery up on my first go. You don't have it on for long - maybe just 10-20 secs per window - so 20 minutes might actually go a long way. - CathD