I have also gotten a reply from bob when I have had questions, so I don't think there is any reason not to believe the info that he gave you. RennTech and Brabus are both very respectable MB tuners that have ties to the factory (Brabus even more so). I don't think you can go wrong with either of them. I have heard of Wetterauer, but I don't know anything about them, so I can't help you there.