From my experience till now,
Even after using the OEM SATNAV for 2 continuous hours it was slightly warm not as in HOT!
The touch screen is not that finger friendly rather it works better with the stylus provided or with the remote control(one has to aim it at the sensor to get it to work).
The lag in appearing of the reverse camera video is never more than approx. "2 seconds".
And till now my unit hasn't hanged, been stuck or stopped working.. Alhamdolillah it's working great!
Thats just my experience