Excalibur is the Grail unlike the other Grail. Sharing nothing in common with the other ICE of it's type (Galahad, Lancelot, Merlin), Excalibur can only be revealed, unable to reveal its buddies itself. And it can often be overlooked, allowing many runners to save a credit or Cerberus "Lady" H1 counter when used with the other Grail ICE. No, Excalibur is a beast of its own. I see it as:
Neutral Trap ICE with a nice effect
Trap, because Excalibur notably has no ICE type. It cannot be broken except by AI breakers.
Excalibur, instead, hangs out with the Upgrades. For a measly 2 credits, Ash 2X3ZB9CY, Red Herrings, and Caprice Nisei, along with other strong Upgrades that typically require a second clean run, become maximally efficient. Excalibur + Red Herrings in a server means that the Runner will pay those 5 credits.
Ultimately, try to separate this card from the Grail subtype. In fact, I would instantly cut it from decks running the actual Grail ICE. I firmly believe this card is strongest when slotted into Glacier-style decks that intend to score in a remote, who naturally run powerful Upgrades to protect them.