I've had a Dynojet QS which killed the fuel for a sec, which was a bit rough and did a poor job in the higher gears. As I changed gears the bike would wheelie and upset the chassis. And it needed to be connected to the PCIII.
I just changed to a Translogic QS which kills the spark softly in the lower gears and quickly in the higher gears, and it's smooth as silk. There's no unsettling at all...just a tiny "bip" noise and barely a change in the drive.
My TL QS is an older model, the latest version is better again. But from all I've read, and been told by mates who own one...the HM QS is the daddy. It works the same way as the TL, it's a standalone unit, it gets plugged into the coils, and it's the best on the market. As used by many of the worlds racing teams.