Hi there,
Many thanks for your query.
Unfortunately you can never be sure how many other people are going to book to travel on an add-on, but in my experience it is very rare for only 1 person to have booked! Add-ons are always very popular, and are a great way to see more fantastic sights.
If you have a particular tour in mind, I can check for you to see how many people are currently booked, before you make a decision yourself.
Hope this helps,
Warm regards,
Cheryl, your editor