I used them twice this year. First car sold was an Audi A4 Avant which they put up with a reserve of £17500, ended up going for £19350.
Second car was a 5 door Mini Hatch, which I think they put up with a reserve of £11,400 and that went for around £12,300 from memory.
Both cars were collected from us within a week or so and they were only here for around 15 minutes to do the inspection, transfer money etc. All money was in our banks before they had driven off.
I think if they are newer cars they tend to be a bit better, my Mum tried selling my grandparents car and even though they supposedly had a bid, the sale fell through. Ended up just taking it to webuyanycar. That was a 2009 Fiesta though so less likely to be wanted by car supermarkets which seems to be where Motorway sell to, at least that's where ours ended up going.