A novel feature in HERE maps is offline mode, which allows you to download maps for offline use, ensuring that you don't run into any overage charges when you're on cellular data.
Since the app is in beta, there are bound to be lingering issues and bugs, like the deletion of navigation voices anytime a cache cleaning utility is run. Nokia mentions that it is close to a fix, which should be rolled out within a few weeks.
To install the beta, head on over to the link below, download the apk file and sideload it onto your device. Need instructions on how to sideload? Nokia has you covered.