I thought I'd just add my two pennith. I have over 2000 clients & eight rounds on the go, I started the business traditional. We are now all WFP. The window cleaners are happier, that's for sure.
As for the clients, I don't think they much care, as long as they consider their windows are clean. Personally, I think it does a better job. The frames get more attention, plus we do a lot of windows that we previously could not reach off ladders.
I think the most significant point is that I have a lot of competition who still use squeegees. If it's better, why don't I lose clients wholesale to these Luddites?