Just to explain the difference from original versions: Amazon version is a special version of Playstore version. Normally Amazon Underground needs to be installed to get it to work. Why? Because all special apps working with Amazon Underground are for free because Amazon pays developers for the time the app is really used. Means all Amazon Underground apps are tracked when you open the app, how long it will be used, when you close it, .....
Thats also the reason why it requires in this case an Internet connection after 30 days.
In short terms: Amazon Underground apps are for free (sometimes with all In-Apps) but you will pay with your private data. If this does not matter for you than it is a good offer. With Navigon here you can save up to 140 € ;-)

This explanation is just relevant for the official uncracked versions!