The navionics app comes with the vectorize enc maps. The app features itself is rather basic but still very good. INavX is a more full featured app, but it only comes with the raster image maps. If you want to use vectorized maps, then you have to pay extra.
For the few dollars, start with the Navionics app. If you want more features, like instrument, plotter, computer integration, then go with iNavX. Both apps are rather inexpensive (compared to everything else yachting).
I recently purchased an app called "AnchorWatch". Check it out too.
S/V Johanna Rose