On the GNS 5870 - mine does not come on unintentionally at all in my flight bag or anywhere else (including jacket pocket). I think there's a bit of a knack to get the finger swipe right - at least on mine. Battery life seems impressive as well.
To be honest, paying out 70 quid or so for the bluetooth device is a pretty small outlay compared to other frightening avionical adventures I have funded in recent years (including that damned Mode-S transponder that nobody except spotters seem to be able to read). I've put a small velcro circle on the GNS so it can sit firmly on the top of the panel with a nice view of the sky. No problems.
At the risk of tempting thread creep, I have to say that my recent purchases of an iPad, Skydemon, the GNS5870 together with the rather neat iPro aviator kneeboard have massively enhanced the enjoyability of my weekend bimbles.