10% bring them, which means 20% use them.
Typically inflated preflight and taken out after last break or landing.
Air mats are highly desirable on the old mattress. They are nice, but not necessary on the new mattress.
There are several sizes and styles, so you may fly a few trips to decide your favorite. Nemo Flyer self inflating is heavier, bulkier and easier to inflate. Nemo Tensor w Vortex pump sack is a light packable option but takes longer to set up.
There is an art to preflight inflation so you have the proper inflation at altitude. JNB is easy because field elevation = cabin elevation at cruise.