I used a similar service a few years ago. We'd already agreed a trade in sale on our old car, but two days before the exchange it got scratched in a car park, so I needed to get it sorted out.
Approaching the franchise holder direct with cash in my hand, it was plain that the business model depends on an inflated price for any work being paid for by an insurance company.
Paying the guy directly cost I think about 30 quid. It was only about fifteen minutes work but he polished out and touched up the scratch so it was all-but invisible, using specialist polishes and experience.
Worth it at that price but I would have been reluctant to pay the £100+ "list price."
I've spent my whole life around that line of work (not in it of course) and the general consensus is that the big bodyshops cost a fortune and do an absolutely horrendous job, which is why so many cars that have had work done by them end up going elsewhere to have it redone because paint is peeling off, the lacquer has gone matt, runs in the paint etc...
Used their services in Basingstoke a few years ago on a Porsche 911 where the bumper had been scratched. It came back like new and was just as good when I sold it a couple of years later. It was black which is probably not the easiest colour to get perfect too. I think these are franchise outfits so I guess it also depends on the individual that does the work but I was pleased with the results.
My neighbour does something similar to this. He gets good results from what I have seen, spending most of his days down at BMW, Audi and Mercedes doing tradeins before they hit the forecourt. He always says that metallic colours are much harder to do, but presumable he still does them successfully because a large number of new cars have metallic paint.