I used a meet & greet company, who were fine for the drop-off, but not for the return. We left from T4 and arrived at T2. The chauffeur took the car to T4, despite me assuring them that we were at T2, but I guess if leaving and arriving at same terminal, it's a good system.

I'm afraid I have used the £34.20 L/T T5 car park for my next short break, as it was considerably cheaper than any other operator. It can be a hassle though.