Friend of mine has a few decent sized trees and was looking to add some ‘aids’ to climbing and descending – ideally with a low skill level of entry. I was thinking about a pulley secured for top rope climbing, or an auto belay, but they are either dependant on a responsible belayer or expensive .. any other ideas (beyond just climbing it, they already do that)? I’m assuming outdoor activity centers have some sort of abseil device that could be learnt reasonably easily to a safe standard as they have to cope with complete novices, but maybe it’s all about (and on) the instructors?

Lots of so called rock climbers these days never get more than 20 feet off the ground. They would never dream of using gear of any sort. They just put one or sometimes two mats on the floor and accept that they will fall. Bouldering is the new black in rock climbing terms. All climbing walls have bouldering sections.

Google is your friend. Try “Bouldering mats”. The world is your oyster.

but they are either dependant on a responsible belayer or expensive

And a chunk of knowledge about how to use them safely.