On dirty glass, plastics etc cold pure don't work very well if you ask me. For example it doesn’t remove insect droppings, tree sap, sea salt, really baked on bird pop, algae/lichen etc very well if at all. That's why more wfp cleaners use some kind of chem boost, scrub pad/scraper, magic sponges and some even hot pure too.
People think using cold pure water is the miracle cleaner but it's far from it in my book 
Yet you think by adding a microscopic amount of additive changes it into one, the majority of wfp cleaners still use nothing
more than pure alone because for all its faults it does what it needs to do.
All the things you have mentioned that are hard to remove can be removed very easily with a bit of knowledge and using the right technique.
I'm not talking about one product in particular so would you care to elaberate?
All of them, your adding an amount the size of the point of a pin to a litre of water even the most concentrated chemical
diluted to those ratios will be rendered useless.
Your basically still using pure but paying the additive guys x amount a year for the privilege but then if it helps your confidence
which is one of the reasons why some find wfp hard to get on with then maybe its worth it.
But to come on here and say it restores the shine on sun damaged upvc does nothing but make the person sound foolish.
That last line wasn't directed at your good self.