I'm confused about how GPS units get updated databases. A panel might
have a GPS unit feeding into a multifunction display MX-20 or
Avidyne or something. Does one need to update both the
GPS and the MFD's databases to stay current? Doesn't this get
expensive and annoying?

Also, must one input the flight plan into both the MFD and
the GPS? It would seem both would need the information.