Well, you're definitely on safe ground installing their mud flaps.  ;-)
But seriously, I agree with you that some of their devices sound really
nice.  I love the concept of being able to use the navigation system
without having to be stopped before entering a destination (and avoiding
the "I agree" all the time), but whether these enhancements would void
the warranty I just can't say.  I think the ones that just involve
plugging in wires would be okay, but you certainly don't want to base
anything on what *I* think.