Alastair,
You're not by any chance putting off getting started because of some of the negative comments you get on this forum regarding the 1st few months of WFP are you.
My advice is go for it, the sooner you get those first few cleans out the way the sooner you will be up & away. I had my first negative comments today but just went back over the windows that had dribbles on.
As for this idea you should convert your round a bit at a time, I can understand why people say it but frankly I didn't spend over a grand to have the blummin thing sat in my garage two or three days a week. Imagine if you went out & cleaned windows trad & fell off & broke your arm while your WFP system sat in your garage, how would you explain it to your missus. "Well I was scared I might get a bit behind so I got back on my ladders one day"". Ridiculous!!!
I have warned my customers to EXPECT the odd dribble, I have told them if they don't it will be a bonus.