I use wfp and i havent got any dirty sills on any of my houses, her cleaner obviously doesnt bend the goose neck and run his brush over the sill then does he! another one who doesnt do a good piece of equipment justice and gets everybody else who uses it a bad name.
Out of 8 of us that use wfp round here 3 of them are crap simply because they dont no how to do a proper job and were just the same when they were traditional,. CRAP
Its like any oyher tool if you dont no how to use it properly your never going to get the best results out of it.