Frodo seems like an extremely powerful and versatile hero. Low threat, decent stats that compliment his ability well (except maybe his which you likely won't be using much) and access to two of the game's most useful abilities: action advantage and threat reduction. In many ways he's comparable to Aragorn (an old classic and one of my favorite heroes), yet arguably better. Suddenly heroes with bloated statlines that have trouble taking full advantage of them (like Glorfindel for instance) can now perform to their full potential from the start of the game and without dedicating deckspace to action advantage cards that you or may not draw. Also the fact that his ability isn't limited to heroes means you can even target allies like Gandalf and Elrond, which can make him act like a pseudo Galadriel. With this ability alone Frodo would already be a very good hero, but the threat reduction is icing on the cake. Seeing as you will more likely than not be questing successfully each round, especially with Frodo's ability to supply action advantage, this essentially means your threat will stay static—barring Doomed cards and other encounter cards that raise threat, of course. This has so many applications, from the obvious Hobbit decks to secrecy decks, you name it. Plus being in Leadership means he shouldn't have much difficulty paying for that one resource each round. All in all I think Frodo has so much to offer to just about any type of deck.
Frodo Baggins
Hobbit.
Response: After Frodo Baggins commits to the quest, spend 1 resource from his resource pool to ready another unique character committed to the quest. If you quest successfully this phase, reduce your threat by 1.
-The Return of the King
A Shadow in the East #2. Leadership.
idk why paying a resource to ready someone was such a common effect in leadership (elrohir, gimli, and now frodo) but there are enough ways to ready heroes that this kind of ability often ends up being more expensive than it's worth. a simple cram can do it for free, and unexpected courage can do it forever for 1 extra resource. there's also the fact that frodo can only ready them for questing, which severely limits his potential
he is able to ready allies as well, but there are very few of them with more than 1 important stat anyway, and many of those already have other ways to ready or quest without exhausting. the threat reduction is neat, but very inefficient for its cost.
so IMO the main reason to use frodo is as a substitute for sam in a hobbit secrecy deck, since he makes it easier to stay under 20 threat and he also lets you play the spirit sam ally, which has a very efficient statline and useful ability