The AdventureCycling GPX files are routes, not tracks.
Routes or tracks format is besides the point. Tracks will just as well have identical display as routes when track points are spaced far apart. Which is the case for the majority of Adventure Cycling routes, causing the display to be in segments of straight lines, not exactly following the roads.
Adventure Cycling is working on upgrading the data format & offering so that track information closely follow the route. An effort started earlier this year with the Northern Tier
The Idaho Hot Springs Mountain Bike Route
is also published as tracks with closely spaced track points to almost follow the route.
They are therefore quite useless for use in GPS, app or no app.
The current route data will not give the exact route to follow. With paper map in hand, combined with GPS location in relation to route, will give a very good idea about location and next steps for navigation.
Another advantage I find useful in the current files is the collection of service points. They give me a good indication of upcoming locations for food, lodging, & other services.