Not required, but its the best mounting option in my opinion.

You could always go for the version that mounts like a satnav if you don't want to lose a vent.
 
one of the best purchases i made for my Leon. The fitment of the insert is really good,and the content of what the gauge does is really good. Its even highlighted that i have a knackered thermostat. Gets a thumbs up from me
 
looks real simple, remove dash and vent then connect plug to the back of obd 2 port , then connect plug to gauge and put the gauge in the vent :) will be giving it ago when i get one :)