This is one of those cases where, for many of us, simpler is better.

You don't need a hundred different functions. If you're underway, you
should be keeping watch and steering, not constantly reprogramming the
GPS to do the next whiz-bang thing on the menu. Electronics should help
you run your boat, not lull you into a false sense that they are
running it for you or distract you from the task.

My two cents: pay some attention to the interface. A larger keypad with
some space between the keys will make it easier to use underway. If you
almost feel like you need to resort to using a stylus in the marine
store, you will have no end of trouble trying to input data or commands
with a fingertip when the boat is underway and bouncing around.