I've seen threads discussing it but not so much the actual book!
Anyway, I'm half-way through (not fussed about spoilers TBH) and honestly, the story of its being written before Mockingbird just doesn't make sense to me. It plain doesn't work without Mockingbird; she's flashing back to characters that the reader is clearly assumed to have some familiarity with, I'd say. God knows what the truth behind it is; it's certainly a readable and even enjoyable novel, so the worry that it would be drivel is unfounded. But the origin story is suspect, IMO.