As of Core + Dunwich through Undimensioned and Unseen this card simply doesn't seem to have a place. 'Add charges to spells' seems like a solid concept, but this card unlike any other in the game is demanding in money, actions AND slots. Money and hand-slot could perhaps be forgiven, but the sheer number of actions required in order to make this card useful are insane. It's 4r + 2 actions + 1 hand to refresh your Shriveling or RotS once.

The card seemingly is meant to bend towards 'hardcore casters' who want more than two spells and want to cast them all a lot, but by the time you've bought this AND three other spells AND burnt one of those spells of it's charges the game had better well be over or you're probably not going to win. You're better off just overwriting one of your original two spells with the third that you need right now. Now, of course, we do have a character who can use Tome actions for free and uses spells! Ah but wait Daisy Walker is a Seeker, and as such doesn't have access to this card outside of Jim teamwork shenanigans...

It's just a huge miss. Maybe one day we'll have someone who can use certain charged spells without using actions, and when that happens this card will probably still be trash tier. It simply is too far removed from viable play in resource cost, action efficiency, and intended function for it to be worth even the deck slot, let alone 3 exp.

The one thing that might change my mind is if in the future we see a big expensive spell with a single, or limited, charges much the way that Shotgun is mad expensive but also dependent on Extra Ammunition

Sounds weird, but this tag is better on easy/standard difficulty than on hard/expert. Sure, the ability triggers more often on tougher skill tests, but the best strategy on a higher difficulty is to do everything you can to minimize the number of skill tests you attempt, or make them auto-successes, with e.g. Flashlight or Will to Survive. When we do attempt skill tests, we want to boost them with sufficient skill cards that we'll actually pass them. So Rabbit's Foot is just going to go a long way to pay off, if it ever does.

Pros

• Good click-compression in decks that are likely to fail repeatedly at certain actions. Like my beloved Wendy at fighting or investigating.
• Synergizes well with other cards with the same triggering condition: List
• Decent install cost.
• 1 -icon to boost skill tests.
• Can form a very clunky combo with Scavenging: Commit Rabbit's Foot from hand to a skill test. If it was an investigation attempt, you are not allowed to retrieve Rabbit's foot after the same test, but in any case after the next successful investigation attempt.

Cons

• The effect is mediocre with the one-time usability restriction per round.
• It takes up a valuable accessory slot.

UPDATE (Path to Carcosa released):

Now that William Yorick joined the ranks, Baseball Bat has found it's love. His ability is meant to retrieve assets from the discard pile. The risk of splitting the bat during a swing is huge (3 out of 16 tokens), so besides Yorick's convenient retrieval method, there are two more investigators likely using the bat: Wendy Adams can reduce the risk of breaking the bat in the first place with her draw-again-ability, and Agnes Baker could use it as a fallback weapon together with her spells.

With the bat in both hands you can hold ground against a group of enemies and deal 2 damage with each blow consistently. The +2 is a dire necessity for investigators who are weak in the knees.

Pros

• Unconditional +1 damage, doesn't use up supplies, +2 for each attack.
• Can be retrieved with Scavenging or Yorick's ability.

Cons

• Two-handed weapon. Don't underestimate this drawback - this weapon competes not only with other weapons, in fact, you should consider any asset which you can not play while baseball bat fills your hands. One could include Bandolier to attenuate this disadvantage.
• There is a high risk of losing it at the worst possible moment.
• Don't waste it to boost skill tests.

The leather coat is the current state-of-the-art proactive damage prevention tool! As a survivor character, i would pack one every time i go out adventuring. The inclusion is harder to justify for other factions as they miss the opportunity to recycle old coats.

Pros

• Leather Coat uses a body slot, only two other cards, Bulletproof Vest, Fine Clothes, compete for this slot.
• Phenomenal install cost. It's a handy throw-away card if you are hit by events which force you to throw assets away. I would argue further that a second copy in your deck is never a dead draw.
• Combines well with Scavenging
• Great click compression, compared to other heal tools like Emergency Aid, First Aid, Medical Texts and Painkillers. Guardians more likely use Dodge to avoid 2 damage.

Cons

• Protects the wearer only.
• Should be played before enemies appear, during a fight it's useless.
• Don't waste it to boost skill tests.

So people wax happy for Jims trumpet in multiplayer, where it triggers very often. Do not be fooled, however, as even though the trumpet triggers 4x as often your allies are taking roughly 4x as much horror in aggregate. In this sense it matches the scale of the game in multiplayer, but it does not exceed it.

Although there is a catch. When Jim plays you can choose who gets the horror. In a 3p game with Jim Daisy and Roland, Jim can tail Roland and play his sweet soothing jazz, effectively moving some of the games horror load from fragile Roland to mentally hardy Daisy and Jim. This margin is where the trumpet is actually super effective in multiplayer.

that being said the trumpet can do work on its own in solo or 2p, provided you have the action economy to afford it. Further Jim's passives make him pretty hardy in hard and Expert difficulties, so don't let his unique asset scare you away from trying him there!