I've been testing this in Daisy Walker with good results. It acts as a second copy of her Tote Bag for consistency, with a few advantages:

• If I see this before the Tote Bag (I won't play both) then Tote Bag becomes basically a Guts or Perception without the card draw.
• It costs 1 more than Tote Bag, but it improves your action economy. It allows you to play something into a hand slot as an additional action, and then if it's a Tome Daisy can use her own ability to use its as an additional action.
• These extra hand slots don't have to hold Tomes, so you could play a Fingerprint Kit, Pocket Telescope, Scrying Mirror, The Chthonian Stone etc. (as examples) without spending a "real" action.

The wording of this card is interesting. Unlike for instance The Hierophant • V, you do not lose your "empty arcane slots" and replace them with hand slots, but get them in addition. This matters for at least two other cards, that have been spoiled, Eldritch Initiation, for which you can happily fill up all additional hand slots, without having to discard any cards. On the other hand, the only basic weakness, Ectoplasmic Horror also won't care, how many assets you carry in hand slots and will let you draw extra tokens, should you go for the Kali-build.

This card has the potential to do what Bob Jenkins does with its ability: having an extra action to play recycled-asset (Scavenging, Joey "The Rat" Vigil)

Another notable synergy is with The Chthonian Stone. Even if not cheap, it can be played without spending an action after it returns to your hand.

Can I use astral mirror's action to play an item into one of my hand slots with salvage?

No. The ability on Astral Mirror allows you to specifically play an asset into one of your hand slots, and does not allow you to play an event, even if resolving that event would put an asset into one of your hand slots.

Sincerely,

Alex Werner, FFG Game Rules Specialist