Yes used it a number of times, it comes out as a last resort for marks and stains that normal cleaning does not take off (quite rare) as for use on self cleaning glass you need to consult the official safe chemical list then make your decision, IME ive never needed anything stronger than pure water when doing self cleaning glass works.
Chris, guttering and sills are extruded in this process the plastic is forced through a highly polished die this gives a microscopic hard shiney outer surface once scratched no matter how lightly the inner "soft" plastic is exposed and will over time degrage, it may not be next week, but over a year or so it will dull and go grey.
I'm just offering up information, your happily cleaning hundreds of houses this way, so carry on as you are, I just wouldn't reccomend it to others
Darran
Ok Darren, can I offer you an example..
3 years ago I picked up a house, large 4 bed with con, front door and step was relatively new but the step was covered in black shoe scuff marks.
I used the stainless wool on the entire step, bringing it up like new, and have continued doing this once every 6 months or so at the customers request to remove the shoe scuff marks.
3 years on the step shows no sign of discolouring, degrading or any other wear and tear. It still looks new to this day.
I think you are mistaking stainless steel wire wool for good old fashioned plain wire wool, which I did try once and you are right, it did scratch and leave the area looking 'dull'.
Good quality stainless steel wool isn't as abrasive, iv even used it on painted doors to remove marks without stripping the paintwork.