Nate Davis looked bad in the 4th Quarter of pre-season games against a bunch of guys (like him) who aren't even on game day rosters right now (or in the NFL at all). Like the 49ers, 31 other teams didn't think he was valuable enough to put on their roster.
He's not even remotely "boom or bust." He's another QB in the long line of QBs (Rattay, Dorsey, etc.) that 9ers fans insist on over hyping to make their desperation hurt less.
Troy Smith will play before he does, as he should.