Let me tell you a story. I was riding from Alabama to Ohio a few years back. To navigate I had a Garmin and my iphone - no paper maps. I had been riding for hours and was in rural Tenn. My Garmin, though fully charged when I started -- died. I kept going now relying on my backup - my iphone. I came to a fork in the road - no signage at all and guess what, no cell phone coverage. All I could do was simply guess which direction to go, pedal that direction, wait for cell phone coverage to resume to see if I made the right choice. And I repeated that cycle numerous time that day. So what did I learn from this?
1. Don't rely on electronic devices unless you have way to keep them charged. I do now - SON Hub Dynamo with a USB port on my bike.
2 I don't like the Garmin and frankly wish I never bought it The screen is small and difficult to read in the sun, the battery life is horrible, and it doesn't do well of redirecting you when you get off track. There are newer bicycle GPS devices on the market which may be better or worse...
3 My iphone, able to be recharged with my USB port, with a quad-lock mounted on my handlebars, works well assuming I can get a signal. I've used a variety of apps for navigating and I'm partial to Kommot (#1)
4 If going through remote/extreme rural areas I always print out paper maps as a back up.