I've nailed down the biggest issue with the Quantum tuned ECU: why the car will suddenly launch itself forward after upshifting to 2nd gear. The VSC is overriding the throttle to prevent wheel spin off the line. This happens on the stock ECU too, but with the stock throttle maps it's barely noticeable. When the VSC releases control and the Quantum throttle map kicks back in, that's why it suddenly accelerates. Very dangerous. I almost rear-ended someone in traffic because of it. I don't know if the VSC is different in the GS430, but it obviously wasn't tested properly. I can replicate it every time.
Quantum also sent me Crown Majesta ECU with part number 89661-3F360. The correct number for the GS430 is 89666-30280. While they appear to be interchangeable, using the wrong part number means compatibility cannot be guaranteed.
Add this all to the fact that I paid for the refurbishing to prevent harsh shifting, and still got really harsh shifting because it either wasn't done right or wasn't done at all, sadly that's three strikes. I'll be asking for a return and full refund, and I recommend all GS430 owners avoid this ECU tuning service as it cannot be performed without compromising the safety of the car.