I don't think prep is worth it, cause it's pretty much shit unless you also have sprint, otherwise it's a dead card so if you sprint and draw it, it's pretty fucking useless. One sprint is great though, while it's dead for a while turn 7 isn't that far off and that's when you'd usuall start losing speed if you've been trading shit for board control, and 4cards is quite a large amount.
Got to 11 on my rogue then lost 2games in a row to fucking crazy decks. Said fuck it I'm starting another, went paladin, pretty good cards, went 4/3, 3losses in a row to some of the most unbelievable decks I've seen in a while(or just really good RNG). Last game I go first, 3 4+cards in hand, mulligan everything, 3 4+cards in hand again yay. He coins juggler, play a taunter on 2 and ignores my 1/1 hero power, I shattered it and kill taunter, he summons a raptor and argent squire, both juggler knives hit my shattered(yay), chip me some more, I get nothing again, he drops flametongue and juggler kills the 1/1 again, chips me again, I drop a 4/8 dragon, he bloodlusts and kills me on 5th turn. Oh, well then. Shaman the game right before dropped 3fire elementals on turn 6, 7 and 8 then faceless copied one that wasn't dead/debuffed on 9. Rough games.
Also last time I draft Divine Favor, I figured eh I might need some draws I'll pick that, other choices weren't very good either, I think it was a novice engineer and a buffing murloc, I figured I could get one card or more out of divine favor so I didn't pick the engineer. I had Divine Favor in my hand in like 6 of these games and I only cast it once, for 3 cards(and I still lost). I had it literally all game in my hand against a mage in the first few games and he NEVER had more cards than me the entire game.