Firstly I can process C Max cartridges right now - so no problems there.
One cartridge from either C Map. Navionics or Garmin will cover all the south coast UK, Channel Islands and northern French coast for more or less the same price (C Max is the largest £ for £).
Regarding tidel data features and functions of C Max have a look here
Navionics can be somewhat cluttered but the levels of data visible at various zoom levels can be adjusted on all three makes so this should not, neccessarily, be too much of a concern.
We are official Raymarine, Lowrance, Garmin, Standard Horizon & Navman Dealers and can supply complete packages from any one of the above.
In terms of (market ready) multi-function units then the Raymarine C Series are your only choice, however both Garmin and Standard are working on similar systems but these will not be fully available this season.
In terms of a stand alone plotter, IMHO at this point in time, I would probably plumb for a Standard Horizon CP175C running C Max - or for multi function then the Raymarine C70/80 running Navionics Gold.
All the best,