I had it during the brief time I was with Crete. It bothered me for about a week, then I totally spaced out the fact that the truck was starting up and shutting off. These days, I sleep so light that it might wake me up every time.
I'm considering it as an option on my next truck, but still favoring a diesel APU at this point. My mind could be changed though withing the next year or so depending on technology.