Most kits are the same (similar), except very rare cases. For example Rocksolidengines in australia who rebuild their engines and replace with quality bolts and stuff before selling them. I don't know of any vendor in USA that does this. Other than these kits, and the branded kits which concentrate more on performance than quality, most engines are same (similar).
I used to stall my bike to stop it, but instead of jerking my bike to a stop, I disengaged the clutch, came to a rolling stop, then engaged it. That was before I worked out my kill switch. I believe the stalling way is better for the engine because the kill switch pretty much short circuits everything to stop the engine, plus it tends to flood the engine