Given that Leitner describes them as an 'expression' of their Entity, I would say that with some limited exceptions, they are actually contained magical items. Mr. Spider is one of the RARE exceptions, since it's very clear that the book directly feeds the person TO the Spider. But something like The Hunter's Almanac is an expression of the Hunt but isn't actually the Hunt itself, any more than Dig would be the Buried actually influencing someone so much as an item imbued with the power of the entity makes them WANT to be buried/dig. Gertrude destroys them, and she knows more than Jon does, which would make more sense as something to do than if it was a completed functional item than if it was merely a tendril that might just find another 'hole' to cause havoc in reality.

Again, something like Mr. Spider, I don't see as being functional but Dig I could see and might make the issue of using them or whether someone might look for them a more mixed bag.