Spent many many miles on one! Darn good dyno never had a problem with repeatability (as people claim is a problem) or slipping! Some of the old (first) ones had smooth rollers and people have problems over 600rwhp with tire slip.
If your using it for tuning just make sure you don't go back and forth between the Mustang (or any load cell) and the dynojet.
Good luck to ya!