in order to use Navigon, i had to make a titanium backup of the paid version from my phone and restored it on my Prime. I do not think Navigon is cleared for use on it yet, which is why it doesnt show up.
The issue with most free navigation apps on android or ios is that they are designed for cell phone that have an always on data connection to pull appropriate data as needed and gets supported by ads.
Navigon being owned by Garmin already has navteq maps that get stored locally to standalone GPS devices. So what they do is import that map data to be stored on the phone's (or tablets in this case) sd card to be used offline. If you can go this route for the 49.99 usd app, i highly reccomend it, I use it alot for travel at work, a data connection is not needed at all for it to work but when you do have signal it will update weather and traffic on the fly and reroute as needed. I hope this helps.
-cheers