TLDR: Ellsworth is a very good for a support partner in the early scenarios that throw many sticky location treacheries at you, but gets generally less valuable as the campaign progresses.

Ellsworth was extremely useful in my group's run of Edge of the Earth, much more useful than I anticipated! Ellsworth can blank several infuriating cards, such as Polar Mirage, Antarctic Wind, and Through the Ice. He can trivialize these sticky treacheries at fast speed , simply costing a supply and exhausting. During and after To the Forbidden Peaks, I maybe used 3 supplies off him at most in a scenario, because sometimes we were already moving from the location or we weren't investigating that round. In this sense, I really enjoyed the flexibility of using it during any investigator's turn, such as if you didn't have anything else to do and your seeker was trying to save their cards, you're able to use Ellsworth to thwart Polar Mirage. Especially since Polar Mirage and Through the Ice care about you being at that location or moving to or from it, if you don't care about going back to that location, then you've relegated that card to an icy crevasse, never to be dealt with again!

Although extremely useful in the majority of the campaign, Ellsworth was just not used in either of the Heart of Madness scenarios. Often, there were few to no targets for his ability, and he was just relegated to a damage soak and target for Miasmatic Torment (Sorry, bud).

Overall, I found Roald Ellsworth to be a solid overall choice for a support partner asset. Man, he is a great choice in Ice and Death and Fatal Mirage, and a decent pick in To the Forbidden Peaks and City of the Elder Things.