I can't comment on CMAP but I've used
Navionics charts quite a bit and really like them. They give you the option of running the SonarCharts in addition to the standard
Navionics charts. The SonarCharts are just really high resolution bathymetry -- I usually flip between those and the navionics charts when I'm in an iffy area to get a feel for what the bottom looks like (on the app I think you can also have NOAA charts as a layer too to compare). The SonarCharts are usually set to a really high resolution that's only good if you're
fishing, but it's pretty easy to scale it back and de-clutter the
screen.
I don't know if you've seen it yet, but check out the webapp -- it'll give you a feel for the charts and some of the routing features.
https://webapp.navionics.com/#boating@6&key=_tfgErwbjU