In my opinion the Ninja God breakthrough is ridiculous, a 30% buff that lasts the entire battle is pretty good. The standard attack breakthrough is alright, the +2 is where it gets an additional tier, having a high chance of immobilizing an opponent each turn without having the barrier up is good. It's worth noting that these books are often for sale in the Konoha Gift Shop for 5000 ingots, so if you take advantage of this then just save for 4 star, if not you're saving 5000 ingots by getting the skill breakthrough from fragments.