We have an iPad II and a newer Mini. Both of them have been upgraded to the current IOS, 9.2, and this has greatly improved the functionality and usefulness of both of them.
We do not use the iPad for navigation. We prefer dedicated plotters-- Furuno, Echotec, Standard Horizon--- for this. But we have a wonderful charting application on them that shows our current position and can be zoomed out to show an area larger than Vancouver Island and zoomed it to show one small portion of our home harbor, all with a couple of finger swipes.
The app covers the entire west coast from Mexico north through BC and all of Alaska and Hawaii. We use it in lieu of papercharts/chartbooks to give us the instant "big picture" something that can take some time to do using the zoom function of the chart plotters. This app also overlays Active Captain, so we have all that information at our fingertips.
Both iPads are digital models so we need no connectivity of any kind to show our GPS position on the charts.
We also use them to get weather information in as much detail as we need. Generally the local NOAA marine forecast is all we require but we can get radar views and all the rest of it if we want. We have weather apps that automatically post alerts if there is some significant change or event on the way or happening.
We have an anchor alarm on the iPads and iPhones which is one more level of assurance.
If we're interested (but we never are) we can call up AIS information but it is not real time so it is no substitute for an actual AIS if has a need for this kind of information.
Add in the other communications capability and social media and the fact I can work on my writing projects on them when we aren't actually driving the boat, the iPads have become an indespensable asset to our boating.
I will eventually need to replace the iPad II with a current model but I'm not going to do that until the II ceases to function or can't do what we need it to do. I've had it for at least four years if not more and so far it has been virtually trouble free. I take it everywhere in the world with me because in addition to being an asset to my work, the fact it can recieve GPS/GLONAS postitioning data with no connectivity means I can use it to find our way around in the middle of China, South America, etc. As long as it's got power and can see the necessary satellites it knows where it is.