I thought I'd share my experience with iNavX on iOS with you.
As most boaters with an iOS device I was quick to download the original Navionics programs. Although hefty downloads they work quite well. Scrolling and zooming is pretty smooth in the Navionics apps. They are a little unstable requiring an app restart now and then, but not very often.
When I learned that iNavX supported a TCP feed I rewired my AIS transceiver into my Linux box and had that start sending AIS and GPS data over TCP, and bought a license for iNavX and a set of (Navionics) charts. This works great, and I'm now able to see my navigation data and AIS targets on my iPad. This promotes the iPad from a good tool for situational awareness to a great one.
There are still a few issues that you should be aware of in case you're considering to use your iPad for full navigation duty, with any app. Depending on your use you may need a waterproof case and have a problem with sun viewability. Also, although iOS supports multi-tasking, it's too easy to accidentally stop an app. In general the large amount of memory that the navigation apps seem to use also makes for occasional crashes. Thus, keeping these apps running for hours on end is not how I personally see them at their best.
Also there is a bit of a downside to the way that iNavX works with charts. Although it is beautiful that you can buy charts online and then download these to the device, it looks as if the charts are stored as "disposable documents." When I upgraded my iPad from 4.3 to 4.3.3 I lost all my charts and had to download them again. As that didn't work at sea without internet I had to fall back to Navionics for a while. Next time I'll make sure I test my chart store after updating the device.