The APK install is not limited by Google Play Store policy restrictions.
The APK version allows DMD2 to run in the background when you go from DMD2 to another app, this allows DMD2 to keep recording a track in the background and increment the trip values.
You should notice that the Play Store in-app purchases and subscriptions are multi-device, they will be available on all your devices with the same Play Store account.
The APK version requires licenses that can be purchased in the Thork Racing website, these licenses are per-device, only one device per license. Also notice that the map license will be more expensive because it is a lifetime license and not a subscription model like the Play Store version.
To download the APK version and view the instructions about how to license it please check this page.