I have had this app for over 8 months now. It is fantastic!
I now leave my hand held gps at home and just carry my iphone. Have my iphone in a water resistant case and the whole lot i am very happy with.
Just last week i got stuck on a nearby island when we anchored near shore only to get back and find the tide had started to run out fast and my boat was high and dry.
The boat didnt float again till 7.30pm and it was absolutely pitch black, my boat has no nav lights and is black and no torch. not to mention the trip back was littered with shallow reef and sand bars.
I used my iphone to navigate all the way home safely whilst my wife held her iphone in the air with here bright light app in action to make us visible to other vessels. It literally saved my life.
Cant speak highly enough for the navionics maps. For what you pay you would be mad to go any other way.