What a booking system has to do
At minimum: show your real availability, block double-bookings, support time zones, send a confirmation, send a reminder, and ideally take a deposit so people show up. Anything less is "a contact form pretending to be a booking system." You will pay for it in no-shows.
Standalone booking apps vs integrated booking
You can buy a standalone booking app and embed it in your website. That works, but you end up with two separate systems: the website does not know about bookings, and the booking app does not know about your services or content. Integrated booking, where the same system runs the site and the calendar, removes that gap.
Booking on Fronts.ai
Fronts.ai includes booking out of the box: Google Calendar sync, time-zone-aware availability, deposits via Stripe, automated confirmations and reminders, and a dashboard that shows everything in one place. There is no "step 12: install a booking plugin".