Hi Steve - no I have not used the kits however I have used the service (Dents Wizard or Dent Doctor). Most of your high end dealerships should have someone they can recommend to you. In the US most all dealers clean up their used cars for sale with as much ding and scratch removal as they can, in fact they even sell ding protection now like an extended warranty. I've watched the guy do my car and they don't remove anything. Holes are drilled in the area they need to get to. For the door dings they drilled in the latch side of the door a small hole that allows them to get in with the tool which looks a lot like a metal riding crop......once the ding is removed they simply put a rubber plug in the hole. You can't see it.
The dings I had were quarter size and cost about 75$ each to remove. I spent about 300 bucks at Dent Doctor before I came up with my Ding protectors. Ugly as they may be, for 2 years now I have been ding free, KOW. (see my gallery)
You should have the service available in the UK to get the dings out. If they are not listed ask a Mercedes or Jag dealer, I'm sure they'll know someone. I'd go that route before doing it myself.
Pat