No you don't need to be a member - but you need a profile to be set up on ClubHub, but it's free (unless you want to race, coach etc. in which case you can add that option and pay).
Yes it is free to all British Rowing members.
But it is also free to people with a free profile, however, they won't be able to access some of the premium content.
Yes, RowHow will work on mobile devices, either through the web browser, or by using the Moodle app