Originally Posted by
Steamer
I actually think a Garmin 500 (or 520 if buying new) works quite well for rando navigation where you are only trying to follow a predefined course.
I made too many wrong turns with my Edge 500 because without maps it wasn't possible to see which of several options (the next road at a 45 degree angle hiding behind the service station after the traffic light) was correct when the signage was hidden or insufficient for the lighting conditions.
I also missed a few turns, because when not on the cue sheet/route screen you can't get a count down.
I switched to an Edge 800 (available refurbished with new battery, new case, and Garmin warranty for $170) which resolved those issues, after trying an ELMNT (cycling roads disappear from maps when zoomed out, can't scroll to see where they go zoomed in, has no street names which help orient you when you've arrived at the same roads other ways, and there were data recording issues) and 810 (crashed on my first ride, lost data in the first week).
While the least bad cycling GPS I could find (.tcx files with user defined course points for things like water, turn guidance, maps with street names you can zoom and scroll, can update maps from openstreetmap, more reliable than the 810, charge while riding with a standard USB cable which attaches horizontally so it can't fall out, convenient form factor) I can't wholeheartedly recommend them because they crash on longer rides. You need to split courses, split rides, and join them later.
And battery life is well addressed by taking an external battery and small charger for overnights (like on a 600K).
I imported a dynamo powered B&M USB Werk from Germany for $54.