There is VERY spotty 3G/4G data service where I live now so I don't use a smartphone for navigation (pre-saving maps is a pain). Even when I lived in the Chicago suburbs I didn't want to use my phone's data allocation for navigation. So, I've always been a Garmin Nuvi user.
Once, while driving around a large state park in southern Illinois the Garmin tried to send us down a dirt road, and across a field. We didn't follow its recommendations. I do wish it had an option to mark a travel barrier ahead, and then reroute.
A similar but larger scale reroute happened to me in Germany, where an entire major highway was closed. I ended up setting the Garmin map (I purchased the German road maps micro SD card) to north up, and just kept taking north and east turns (the general direction we needed to go). We eventually got to our destination. There my smartphone simply couldn't get data (I was unwilling to pay the cost).