ive never used one but i bought the gardiner scrapers that fix onto brush but didnt find them very good to be honest.
i use the edge of the brush for stubborn birdmuck,beepoo,fly poo.once the window is wet its the best method although i will only use it as a last resort.normally ill look over the windows when i first pull up and squirt any muck with pure first and let it soak while im cleaning the other windows then 9 times out of 10 it just comes off easily with a few scrubs.