Dont like the thought of drilling a hole in my boat. Anyone know the good or bad of thru hull,in hull,or transom mount for formula 335 fastec (step hull)

This one is in my Cig, mounted inside 4" up from center of keel on starboard side 12" in front of engines, accurate readings across the board and at all speeds.

http://www.airmartechnology.com/uplo...chures/P79.pdf