In principle, nothing precludes you from installing uncertified equipment in a certified aircraft if it's to be used as secondary reference only. However, if you are going to install it permanently and wire it to the electrical system of the aircraft, then you need a Part 66 guy to do it, but it shouldn't be too expensive, especially if you piggyback it to an annual. On the other hand, you may exploit the non-permanent installation exemption if you already have a power socket and power it from there, or if you buy the backup battery (which is part of the kit for the certified G5 only) and just charge it before the flight. A fully charged battery lasts 4-6 hours.