Bear in mind that when a car GPS re-routes you, ALL the roads are good for driving a car. Excepting the common problems of the GPS not knowing that a National Forest road (US) is dirt and covered with snow in May. Or that what it thinks is a road is really a set of train tracks (happens around here frequently, or so I read). Even auto units screw up often.

A bike GPS needs some form of data base as to which roads are bike friendly and that's not in a typical map data. In theory, the unit could do q web based query of Ride With GPS, MapMyRide or Strava heat map to search for routes that are local and popular with cyclists. That's a Google'ish type search and I could probably live without it. Certainly cell data and BT intensive, thus battery killer, etc...