I've been using them since 2023, and they really do increase the replay value of games, but I think there are three problems with them.
First, they should only be used in games you've already finished, because otherwise you focus more on getting those achievements than enjoying the game. Second, many of those achievements involve a fairly high level of difficulty, which makes it not worth mastering the set.
For example, they give you a challenge to defeat a certain boss without taking damage, which is understandable, but then they add extras such as not being able to use recovery items, having to be at level 5 maximum, and not being able to use certain weapons or spells, etc.
I can understand that many people like these challenges, but in my opinion, they should be separate sets for hardcore players.
And finally, they still haven't added an option to unlock them in offline mode.