I used to use Promech, but the guy just pissed me around so much - once left my car with him for a week with a list of 5 relatively easy things to investigate / fix. When I picked it up, he'd done nothing that I asked for.
Mate had a R33 GT-R, the engine blew a turbo and required a full rebuild. That took the better part of 6 months! Then later he found that the turbos had not been installed properly, with 1 opening the wastegate way ahead of the other.
There was also a problem with tuning a plug-in ECU, can't remember which one - might have been a Link -, but Vince couldn't tune it so he pressured the guy to buy an APEXi (I think). Later, 'Eric' managed to easily re-tune the original plug-in.