For a let apartment the governing problem is key circulation rather than resistance. Guests, cleaners, agents and owners all handle keys and access cards through a season, and no amount of hardware quality helps if the number in existence is unknown. A cylinder change whenever a set is not returned directly, built into the changeover routine, is worth more here than anything else an owner can buy.
The balcony slider is the physical item that matters in those buildings. It is the largest opening in the unit, it takes wind and salt directly, and it is frequently the door nobody thinks of as a security element because it is several floors up. On the exposed elevations it also stiffens noticeably faster than the front door, and a mechanism that is hard to operate is one that eventually stops being locked. Servicing it is straightforward lock repair; replacing worn running gear is a small lock installation rather than a new door.
In the old village the brief is different and considerably gentler. These are small, long-standing properties with original joinery worth more than the locks in them, so opening without damage matters and improvements sit best on the internal face. What they do need, in common with the apartments, is corrosion-resistant fittings anywhere outdoors — a village gate lock on this coast has a short life if it was chosen for price.