My experience has been choosing the wrong day to attempt the Five Ferries route. We were just two, but were refused passage, offered the slim chance of getting the next ferry (too late for the full route, and CalMac didn't know if the next ferry even had bike spaces!) and the possibility of not getting the ferry back (sorry, we can't guarantee that you'll get a bike space off the island, no we don't know how many will be available, and no, they can't be booked).
If we'd just strapped the bikes to that well known bike accessory, we'd have been able to book space...
Given the lack of the ability to book bicycle spaces, my attempt at the Hebridean Way with the family included me booking a car, then cancelling the car (for free) when it became clear that all of the family could get their bikes on the ferry!
For a single traveller, able to take the next ferry with ease, it won't be an issue, but if you're travelling as a group, or have to make a particular ferry it's a nightmare...
One solution is to turn up very very early (first come, first served), but if you've reliant on public transport connections that may not be possible.
Another would be to sweet talk a driver to let you throw the bike in their vehicle and walk on as a foot passenger.
Robert