How easy is it to make a connection to the aircraft pitot-static system?
It's very easy to connect a component to the pitot and static systems: It's literally just basic plumbing (install a T fitting and connect the lines). For IFR certified aircraft a static system test will also be required (and a pitot pressure leakdown test would be advisable if the pitot system is opened).

The regulatory issues surrounding the installation are more complex regarding what kinds of devices may be installed on a certificated airframe and under what conditions they such devices could be used as a primary or standby reference for flying the aircraft, as Ron alluded to.