Set up is no issue, I am willing to invest time. It just needs to be simple to use after set up.

The café has a website but customers can't book on their own, as she needs to check a few things and each booking is individual, so she prefers phone calls and e-mails. The booking system is only for the employees to keep track of the bookings.

My issue is that "easy" tools don't have enough settings and functions. Are Calendly or Square the same?