In solo play they can be quite useful if you are building a very dedicated Gondor swarm deck, especially with the use of A Very Good Tale, where you can abuse this card high printed cost. Otherwise if there a lot of Gondor allies spread across a Fellowship it quickly become trivial to play them even in a non dedicated Gondor swarm. They have a good chunk of Hit Points and with Visionary Leadership in play they can quest for 2 Willpower so not bad for an ally that might have been free or payed 1-2 resources.

There are two things which are very more often than not the gameplan for Gondor decks: Swarm allies and then play A Very Good Tale to swarm more allies. Citadel Custodian helps with both those goals excellently, being often free or near free, contributing decent stats for such low cost (especially when you factor in cards like Faramir or Visionary Leadership) and still being able to tell A Very Good Tale due to its printed cost of 5.

In multiplayer, this ally gains even more value since there are just a bunch of Gondor allies who are very popular and might even be run outside of Gondor decks, such as Warden of Healing, Faramir or Errand-rider, thus further diminishing its cost. Not a card that will carry you to victory on its own but definitely an ally that excels in the decks it fits into.

Rating: 6.5/10

Decks of mine using Citadel Custodian

All my card ratings