Entered my registration on Thursday last week and my car has just been collected (following Wednesday). The company I found via the site was Crosslands vehicle sales who were very pleasant to deal with, he had a quick look around the vehicle and service history and that was pretty much it. He pointed out a couple of little marks I had missed but quite happy and transferred payment to our account.
I ended up getting £15500 for Porsche which was £700 more than I had been offered by another well known car buying company and of the 9 offers I received through the site only 2 were less than what I had already been offered elsewhere.
My only criticism would have to be uploading the photos. I had a few issues with this but did eventually solve by reducing the size. - Might be something you could look at.
Overall I would have to say a great experience, not quite what I had been trying to get privately but certainly a lot more than I could get elsewhere.