Based on the evidence we have (which was not much last season), he appears to be better than Cook at center, but we really don't know if he's better than Kowalski.
The contract doesn't force Dallas to start him, which means a quality center could still be brought in, and it doesn't even assure his spot on the roster because the signing bonus is small enough to absorb.
Doing this simply means Dallas signed him for less than it would have had to tender him AND the Cowboys have him wrapped up for next year, too, if he proves to be one of the top nine or 10 linemen on the team.
I'm very happy with this signing and its implications.