I am genuinely interested to see any damage it does.
I'm only interested in UPVC and glass though tbh.
Obviously it's fine on cars, that's why it was designed.
Can't think of anywhere else I'd use it...
Just for clarity, I know TFR is acid but is it caustic? Is there a difference?
Darren, i've no idea about the do's or don'ts of TFR's on UPVC or windows, but i can tell you 100% they DO NOT work on vehicles, even though thats what they are designed for. If they where i would not be (an neither would anyone else) using brushes and sponges on them if the TFR worked !!! We just use soap to make everything glide easier !!! I clean a good few vehicles.
Brake dust on alloys though CC? I've not found anything better...
To be honest i've never had a problem getting it off with just soap and water, or even with my wfp System and brush. But there is an acid we use for alloy occasionally, its probably about as environmentally unfriendly as you can get !!! But if you spray it on an alloy (truck ) tank, or a wheel then guaranteed they come up like you've been scrubbing them with brasso. This won't apply to modern alloy wheels which are painted silver and have a layer of laquer on, but all the other stuff, yeah its great. I've no idea what harm it does, but it stands to reason that it at least "takes a layer off".
Going back to UPVC, in my opinion if a solvent is not removing ingrained dirt, then it needs a layer taking off, whether thats an abrasive cream, fine wire wool whatever.......i've yet to find anything else to truly whiten up or rejuvenate UPVC.