The previous owner of one of my Range Rovers got him to fit the LPG to the car. That was a few years ago. I have had him service it a few times (no one in Scotland can do that system so it is just as well I have friends I visit regularly in Preston!).
I have not had any problems and he always seems to have enough work to keep him busy! The premises themselves are not 'customer friendly' but there is a nice pub in the village that nip in to while he carries out the service! I doubt you will be waiting around though.
I would go for it! However, please avoid the 18 December as I am booking the Range Rover in for a service!!
Craig