Anyone had any experience of how it goes on? Our door to the yard is fine but has us a little marked and I’m thinking a lick of black paint over the white would look smart.

Are you talking about applying paint to a uPVC door?

I’ve seen it done well by professionals and poorly by amateurs.

Never seen it done well by an amateur.

I have no idea if anyone does it, but UPVC doors look like prime candidates for something like the wrapping process sometimes used on cars.

edit: https://www.framewrap.co.uk

Sorry, just kind of thinking aloud.

You can restore white upvc with wet and dry sand paper..
With a bit of time and effort you can get it almost looking new

We’ve done both sides of our old uPVC door recently with Dulux Weathershield Multi Surface and Rainbow Chalk Markers The One paints. Both gave an acceptable finish but Dulux was far easier to work – much more viscous. Unfortunately the colour range is more limited but if you just want black then it’ll not be a problem.
Use a sponge roller and build up in really light layers. As the surface is so flat and smooth, every imperfection stands out