I picked out the four record attachments as the best designed cards for the mono-sphere archetype the designers were trying to push during the Against the Shadow cycle. What's so well designed about them, you may ask? Well, for one thing they're not absolutely exclusive - you can play them outside of mono-sphere, but for a higher cost. This makes sense for the setup, because it means that the powerful effect is generally available, but is more easily accessible to someone who chooses to focus on one sphere only rather than blending them together. Furthermore, it provides mono-sphere in particular with access to an effect which is likely more useful for them than it is for dual or tri-sphere setups, because a mono-sphere deck is likely to have a wider variety of events it may wish to recur in its chosen sphere, while a multi-sphere deck will have a mixture from multiple spheres. Which leads us onto the design of the cards themselves - they give tremendous flexibility since they allow you to choose any event in your discard pile at the moment you choose to discard the record - so long as it's an action not a response - in contrast to other recursion effects which would have you choose a specific card to return to hand or shuffle back into your deck. Moving the event subsequently to the bottom of your deck neatly limits the recursion (so multiple copies of the record or attachment recursion won't allow you to immediately recur the same copy of an event multiple times), but in turn allows for additional recursion if you have enough draw or fetch effects to retrieve the event from the bottom of your deck. And then there's just the general uses of recursion - it works for playing events multiple times, but it also works very well for any strategy which involves discarding a lot of cards (such as Noldor or Caldara) since with a record in play it's like every (non-response) event in your discard pile is in your hand. Between the flexibility, the power of recursion and enabling some different playstyles for mono-sphere in terms of your attitude to your discard pile, I'd say it's hard to argue the records aren't incredibly well designed. All that remains is to examine the sphere-specific aspects of each record.
So the Book of Eldacar in . There are plenty of events which are worth recurring, whether you want attack cancellation with Feint or Thicket of Spears, direct damage with effects like Skyward Volley, Pursuing the Enemy, Hail of Stones etc, or any other weird and wacky things you may think of. Unfortunately you can't use the Book to recur Foe-hammer, since it's a response, not an action. There are to my mind two significant flies in the ointment however - one is that if your deck is mono-, it probably has enough combat power that it doesn't need to depend on such tricks, much less repeating them over and over. The second is the existence of Háma, who already recurs events by attacking with no additional setup required. Admittedly he then forces you to discard cards, but you can bring them back again later if they're events, you probably don't need everything, and since unlike the Book, Háma can recycle Foe-hammer, it's easy enough not to run out. Of course Háma can only attack once per round, so maybe you run the Book as well to increase your recycling potential, but on the other hand you could simply run Rohan Warhorse to get additional attacks out of Háma. That said, Háma may be better suited to a multi-sphere setup rather than mono. In the end though, for me it mostly comes down to the initial point - I don't play mono- that often, preferring to mix it with something else, and when I do, it most likely means a very focused combat deck which doesn't need to recycle its events to kill everything. Add in the Háma factor and I'd view this as the least valuable record, certainly my least used.