It's the free "Navionics Boating USA" app. I have it for my IPhone. It works great in my opinion. I can mark spots from a map and use the GPS with the app and get to the point I marked. This saves me time from having to go to my sonar and putting in the coords. I just go to the spot using the navionics app and then I mark my sonar when I get to that spot.
I'm not sure about the paid app. I think it costs money because you get Canada also. Not sure.