Navionics App - Q's

Does anyone here have this app on their phone (ideally iPhone 4)?

How well does work? Is it worth the $10?

Link to app: http://itunes.apple.com/us/app/marine-lakes-usa/id377908737?mt=8

From the reviews, it seems to be a hate/love app.

I have it on my Droid. Don't really use it much, but what I think it is easily worth it.