I think the 4inch Unger ones are the top of the range
versatile but you have to take care when changing the blades.
Because you can open and reverse them you can clip them into a standard squeegee handle they are tops for big initial cleans, and of course you can then attach them to extention poles.
There is the retractable stanley razor scraper, this is a nifty one too, smaller so not as useful for large areas as the Unger one, but ideal to have in your pocket for nipping off recalcitrant bits of bird poo!
Got to be careful changing these blades too, and they can be fairly fragile in use.
The good old stanley scraper, with an ordinary stanley blade in them is now a useful tool for me.
As I am a WFP'er now, I find it great to wedge into the end of my Unger poles to get off the odd bit of dried on bird poo from upstairs windows.
Not a lot of use for WFP users with other poles, but with the Unger ones it fits in just great
Regards,
Ian