Anyone heard of this Tuning Company? https://www.performmaster.com/gt-63-c192/

Haven't heard of them, just got into researching ecu tunes as well as i just got a brand new AMG GT55. From my knowledge so far best you can do to avoid warranty issues and get the best bang for buck is to go with a renntech tune.

I'm looking at this vendor as well, but can't find any information on them, not sure I'm willing to take the risk.

Or run a second ecu.