I have been looking at this card and initially thought it was pretty great. Spells often run out of charges faster than you would. I often see Mystic become super powerful when they get their spells out, but then become pretty useless when they run out of charges.

Having an extra arcane slot seems useful and being able to recharge spells seems very useful. It allows you to run a more diverse deck.

That being said, 4 resources and 4 actions to recharge Rite of Seeking seems like a poor substitute for say 4 resources and 1 action to play a second Rite of Seeking.

What is everyone's thoughts on the BoS?

Depends on for whom. Jim does perfectly fine alternating between spells, equipment and his pretty reliable statline. Agnes not so much. I think of book of shadows less as a permanent source of charges on spells and more like a stopgap. I'm going to have two copies of shrivelling with Agnes, but if i only have 1 out and am low on charges then i can spare an action or two to extend its life while I look for my other copy. Also, the extra arcane slot is REALLY useful with her. I generally don't use scrying in a 4 person game unless it's on my 3rd (or 4th) spell slot with her. Seeking and Shrivelling are just too useful. And if u don't expressly need one then the other is for clarity, which she needs.

I think there's a good reason Daisy can't take Book of Shadows

I'd agree with Vermillion - it's not an efficient primary strategy to keep your spells charged, but the charge count isn't going to get you through an entire scenario. That goes from "I need to draw Shrivelling" to "I need to see both my Shrivellings" which is far less reliable. It also makes a good backup plan for those games where you seem to keep pulling all the enemies whether you like it or not, or Rex goes and triple-tentacles an investigation turn (I actually did that last weekend).

I think it may get more valuable over time, too... Right now there's something of a shortage of general utility spells so the extra Arcane slot isn't a huge benefit, but that will probably change. If/when we start getting more powerful spells with more limited charges its value will go up dramatically as well.

While we are telling stories, we had one game where Lita Chandlier ended up on the bottom of the investigator deck 3 times in the same game. We noticed when we picked up the deck after using Old Book of Lore.

As we get more spells, I'm sure a 'support' spellcaster style will become more possible, running clarity of mind and other things to keep other investigators topped up. In that sort of deck, playing the book becomes plausible as you may have 'spare' actions to charge spells because you're not dedicated to investigation/fighting expressly. MAYBE.