Was in the very same boat as you. Purchased a cheap used Garmin and found out the hard way. Now I just use my android phone and import all my routes to OsmAnd. Works perfectly and it's free.....cell coverage or no cell coverage.
I think this is the way of the future. Smartphone apps that do everything, and more, that most stand alone GPS units do now. Osmand. CoPilot, etc are a good example. I would imagine that the big outfits like Garmin and TomTom are concerned. If the auto companies ever delink their satnav systems to many other, desirable, options I would imagine that their sales of that option would plummet.
The problem so far, with phone apps, is that they suck battery power but that will be overcome.
I have put off buying a newer GPS unit. Waiting until a real good phone app is available. I don't expect that I will have to wait very long. I have used my old (2008) TomTom920 in some 25 different countries and it has worked at about 95% effectiveness. Perfect? No. But neither are the $7-800, motorcycle, specific units.
Rod