I'm not sure why other philosophers dislike the notion of relative identity. I find it unattractive because (1) it's a more complicated notion than absolute identity and (2) I don't see how the added complication solves any problems or illuminates any distinctions that we can't solve or illuminate without it.
Take the example you gave: two printed copies of Animal Farm. I say that those items are absolutely distinct. I take it that relative-identity theorists say that the items are identical -- one and the same individual -- qua story but not qua printed book. But why not say, instead, that the two printed books are type-identical tokens -- absolutely distinct physical tokens of a single story-type -- just as multiple distinct tokens of the single word-type "tokens" occur on the screen you're now reading? The type/token distinction is already available and independently motivated. So I see no reason to invoke relative identity in order to understand the example you gave.
At any rate, the reasons for accepting relative identity that I've seen don't persuade me to accept it. Perhaps there are good reasons that I haven't seen.