Use them all the time, commercial and domestic, less mess quicker cleaning,
Battery is about 20 mins continual use, each widow take around 15 seconds to clean turn off between each window.
Never lost a job using one, in fact i have several customers that have them sitting in the house unused while we use ours

So whats more professional, a guy who invests in the latest technology, does a quick clean no mess job, or the guy who arrives with a stick of brass channel and rubber strip? Costing around £2
Answer - neither both get paid to clean a window, weapon of choice is down to the individual!
and having used both the end result is the same - perfect.
( just less hassle with the karcher )
Darran