On the customer's page
Below 'Next visit', there's an 'Add to calendar' button. It opens the right sheet on iOS, Android, Mac, or Windows.
It stays live
Because it's an iCal subscription (not a one-off download), the customer's calendar updates whenever you change their schedule. No more 'wait, weren't you coming Thursday?'
Commercial customers too
Hotel housekeeping managers, restaurant linen managers, office facility managers — the iCal feed gets the whole property's visits. Put it on the office shared calendar.