When I rode the GDMBR last summer, I used and Android phone with the same two apps. Maps.me was my primary app and covered the whole route with the exception of part of the Wamsutter section. I also had photos of the Adventure Cycling GDMBR maps on my phone for reference as well. I wrote a post on my website after the trip about smartphone navigation, if you want to read more.
https://wanderingbybicycle.com/1477-2/