This application build on the top of my another free app, My POI KML Viewer, which means that you will be able to open your own KML and KMZ files and navigate to selected waypoint, both online and offline (if selected navigator allows offline navigation).
In addition to this, My Hot Springs USA allows you to purchase different collections of the USA hot springs coordinates and description. Once you have downloaded collection it will stay on your phone, so you would not be depend on the network access.
Collections can be purchased individually by each state or altogether, which will be significantly cheaper if you more than one state.
You also will be able to download free sample collections.