The obvious card to compare this to is Chicago Typewriter, since both are 2-handed, 4 XP rogue weapons.

1. Cost: The Beretta is slightly cheaper to play.
2. Damage and ammo: Both can do up to 3 damage per action once they are in play, and both have 4 ammo.
3. Combat bonuses: The Baretta gives a bigger upfront combat bonus, while the Typewriter allows you to use up extra actions to get +2 combat for each action spent (this might seem terrible, but it does increase the total damage output for very high fight enemies who you would otherwise fail fight tests against). If you need to ready the Beretta, this takes away the combat bonus advantage of the Baretta over the Typewriter, since you have to succeed by an additional 2.
4. Risk: the Baretta has a glaring weakness of requiring exhausting it to fight. It can ready again if you succeed by 2, but this could get you in the sticky situation of missing and having your Beretta "jammed." So it's good to have an escape mechanism if you are using the Beretta (which can be as simple as high agility to evade).

If you do the math on damage per action (factoring in the chance of missing, based on the token pool), the Beretta deals more damage than the Typewriter when only one shot is needed per round, especially against higher fight enemies. The one attack per round might be enough for some parts of the game, especially if you are using a "hit and run" strategy focused on evading enemies and getting clues. Because of the +4 combat bonus, it offers a very high chance of dealing at least 2 damage. But the Typewriter deals more damage if you need to attack multiple times per round. So the choice depends mainly on what type of attacking you will be doing with your investigator. Of course, you can take both, and play the Beretta earlier in the game to fight lower health enemies (especially 2-3 health enemies), and play the Typewriter later to fight high health bosses.

15 Cards in hand is very unlikely unless I've missed something that gets you a huge hand size boost and even then you're unlikely to both fill the hand and want to hold them all.

10 is doable with the new size boosters (Looking at Harvey Walters) but a card in hand is one you aren't using

Quite a few Seekers routinely hold 5 cards for their Educational edification however. It's not fast or free but if you're playing with a big hand anyway you might want this over the Magnifying glass (it's a Tome)

EDIT: I missed Dream Enhancing Serum which could get you some very big hands -you're probably still better off just throwing the cards at checks most of the time.

Game designer Matt Newman has confirmed on Twitter that The Watcher’s Grasp effect includes causes the Spectral Watcher to exhaust: “Q: Does the Spectral Watcher exhaust after moving and attacking with Watcher's Grasp? If that's the case, it would not attack later in the enemy phase, right? A: Yep!”

from mobile.twitter.com

A much, much cheaper alternative to Sign Magick. Not only does it cost one less resource, you also don't have to spend the resources and action playing the spell you just made room for. And because of its reaction ability and the fact that it doesn't provoke AoO, it's effectively fast if you only play it when you need its effect. This is a card that has so much convenience going on that, if this were a competitive game, it would be considered broken. We'll see how it plays out in practice, but it's very appealing for decks that can take it.

Who benefits most? Mystics like Akachi and Agnes, at 5 will, can use it to replace events that allowed them to fight or evade when their spell slots were full. Mystics whose will is closer to their other stats see less of a benefit, but still might like that third-slot versatility. For non-Mystics, who has the will to make it work? Parallel front Daisy with original back can pump her will to awesome proportions, but that fills her hand slots. Carolyn might actually be the non-Mystic who gets the most from it, as she has decent will and generally free hand slots. It allows her to evade cultists and pick off rats which she normally can't do herself, so it's pretty useful for her too.

Very compact card, performing a lot of functions. Interested to see this in action.

Guardian economy in an uncontested slot? Because let's be real: nine out of ten times the investigator who needs the most help offering for their assets will be the guardian. In a Sister Mary deck this feels like an auto-include, since it only needs two tokens sealed to beat Emergency Cache, with the potential to far outstrip that in terms of resources generated. It remains to be seen if someone like Roland or Yorick will be provided enough tools to stuff the chaos bag with bless tokens and make this reliable.

It also remains to be seen if someone like Carolyn or... Skids, I guess? could make use of it as a support tool for the other members of the team. I can't really think of anyone else who could take it (besides Dunwich, and it's probably too niche unless they're going full bless) and not really need the economy; Diana can take it but she wants her arcane slots, and there isn't a seeker/guardian that I know of, or a minor guardian other than those above. Correct me if I'm wrong.

So the power here depends on whether I can load the bag with bless tokens while fighting, moving, and protecting my allies; if I can (or if I'm Mary) it's arguably better than emergency cache. If I can't, it's probably a miss.

Final note, it can't go under SttP, but that's a pretty minor hit. Excited to see it in action.