nav 50 or comand

[ucb]

My dad is speccing a E coupe and was wanting to know if he should get COMAND or the Nav 50.
It looks like the Nav 50 is just a directional nav system wheras the COMAND is a map display and also TMC functionality. COMAND includes more multimedia options as well.
So I suppose the questions are:

1. Is either system worthwhile compared to eg a TomTom or Garmin?
2. How is the COMAND different to Naz 50?
3. Is the COMAND significantly better than Nav 50?
4. How easy are they to update? is it really just a case of insert DVD and that's it?

Thanks for any help.