I've put about 25 miles on the car since the install. So far I have not had any engine problems except for when I forget that the button actually works and start playing with it
I had to get an inspection today and didn't get any trouble from the auto shop or get any feedback of something being horribly wrong. It's only been on for a few miles so that doesn't necessarily much.
It does seems like it takes a second longer for the engine to shut down when using the kill switch vs key off, I'll have to investigate that more. I do like that the ultragauge reports properly every time now with the engine killed. Before, when I would key off, the ultragauge would stop reporting trip and short trip MPG about 50% of the time.