I have uesd Navinics for the past 7 years and find that they keep coing up with better ways,and improving there charts. I currently have them on iPhone and iPad. If you have not seen them on a iPad way cool.
I'm going to have to try them on an iPad. I've been trying to figure out a good/dry way to mount one on my 18' CC for fishing, exploring, etc. I've used GPS Motion X on the iPad and its is pretty cool. Has access to some offshore charts. Not much inland. For about the cost of a drink at Starbucks its worth downloading even if you just tinker with it...
The Navionics cards can be used on many chart plotters, there are a few different Windows PC software titles that read in Navionics SD or CF cards, and there are a couple choices for iPad / iPhone apps (that don't read physical cards but download the equivalent charts). So there is a lot of flexibility in terms of where / how you use Navionics charts.
For inland lakes of the USA and Canada, Navionics has some collections good for fishing and navigation. Google a phrase like "HotMaps Premium and Platinum lake maps" and that brings you to various sites that discuss or sell Navionics charts (my own company among them, but I'm not plugging here). And in the iTunes App Store if you type in "Marine Navigation" you get search results like iNavX (which downloads re-sold Navionics Gold and HotMaps and Fish N Chip) and Navionics very own app (which inserts its high def chart into the app itself) and other interesting choices for non-Navionics charts.
We used the mobile Navionics app on our Galaxy tablet for the whole of our 7-month cruise last year. We actually just put the tablet in a gallon freezer ziplock bag and mounted it on a clip-in mount that we made from a small screen mount. It worked out perfectly.