I think you need to be very careful at which tables/games you decide to utilize this concept with and how. It has strong storytelling potential and aligns suitably well with a setting framed around the traditional Law vs. Chaos setup; this is idea is prominent in Three Hearts and Three Lions and Moorcock's Elric series, both being prominently featured in Appendix N as part of the history of D&D. The warden's presence, in my opinion, should not be used to undercut the achievements of the party or make their victories feel hollow, but it should encourage them to think more deeply about their role in the setting's cosmology. However, because the warden is explicitly guarding a moral axis rather than an ethical one, the setting may have a natural tendency towards entropy until the warden is confronted.
If players pass through the world as questing heroes doing whatever they please in the moment, the warden will likely have little effect on their disparate, individual adventures, diluting the reason for including it as a mechanic. However, if players try to establish themselves as their power increases (i.e. domain-level play), they will be inherently opposed to the warden's will since they are now operating as a locus of law and stability. As long as there is a way to deal with the warden in a way where the party is able to make a meaningful choice, then there should be no issue. On the other hand, if booms and busts continue to occur regardless of their attempts at stabilization, they may become frustrated with what they perceive to be a lack of cosmological agency.
The presentation of this supplement is clean and easy to follow, no notes there.