Is the 10 viewer cap on the Casual User plan a hard limit?

No. A little-known fact is that the 10 viewer cap is not a hard limit; people will not get blocked out of your stream like they do with Join.Me. The 10 viewer cap is purely honor system, and it’s acceptable for you to occasionally go over the limit. If you consistently go over the limit, you might attract some polite inquiries from the administration.

https://www.tigerdile.com/frequently-nommed-questions/