We have had a topping lift on Delphy for 10 years. fitted to a block at the top of the mast, with a 2:1 purchase to adjust length and a simple cleat on the mast. Certainly you don’t want to fall onto the boom with the lift engaged, and yes in theory you could damage the mast this way, and you need to set it loose enough when sailing for it not to interfere with your sail shape.
We have never regretted having it. Our boom seldom if ever crashes into the boat, and it makes reefing easier.
‘Boris’ W6330. (cruising secretary)