As others have noted, this is a great move for the Celtics, but a terrible move for Barbosa. If I was his agent, this is not what I would've recommended.
Quite frankly, there aren't enough minutes for Rondo, Terry, Lee, and Bradley once all four are healthy. There truly are less than zero minutes for Barbosa.
Still, given that injuries will occur, this is a phenomenal move for the C's. Is he less of a pure PG than some guys out there? Sure. But he's way more talented. And that makes a huge difference.