I have used both S4U and Colin a few times and would recommend both, although S4U seem pricey.
I have had a few runs done on the rollers at S4U and yes they use a big fan in front of the car to simulate air passing over the car as on the road.
HTH Andy
I know that feeling, since re-map nothing but problems engine keeps cutting out so gonna try a new crank sensor as I have read plenty of others having the same problem due to a faulty one.
Blimey, this came around fast , I should still be there, car not looking its best at the mo though, had to rush a couple of jobs to prep for re-map which is this Friday