So far I have not posted to this thread as I do not have any
help to give, but, now that I've read this posting, I have bought and used one of these kits, but only to paint PDC ie parking sensors and it worked out very well.
I applied two coats of a suitable primer for my colour (Audi Deep Sea Pearl effect) to give the correct base coat in case that made any difference to the final appearance, followed net day by 2 coats of the colour, followed maybe after 30 minutes by 2 coats of the lacquer.
I suppose as you are also painting a part while it is not fitted to the car, you can take more risks and be able to support that part or parts so that you can spray them indoors away from any dust etc and spray them from all angles.
Edit:- have you checked the price from your local SEAT
dealership - or are you only using that ebay listing as a sample of these spray kits that VW Group sell?