If you are wanting to book for Easter weekend, it will be very busy.
Our friends have booked but have asked us to confirm their reservation if we pass as previously one of their bookings seemed to disappear in favour of a local!!
In our experience restaurants in Mallorca are not set up as efficiently as UK restaurants for handling bookings etc online (and we've also noticed relatively few of them have a website). Even Stay - which is pretty high-tech as restaurants go - doesn't seem to respond to email booking attempts. For that reason we always book either in person or by phone.