I like Koufos fine, but I don't see him as a difference maker, and I don't think he has much upside. He can give you 10 pts and 8 or 9 rebounds if you play him starter minutes, and he can defend the center position OK.
So in my mind he's like Zeller. Mediocre as a starting option, pretty good as a backup. Perhaps less likely to get overwhelmed physically like Zeller just did against Mozgov, but Koufos isn't overwhelming by any means in terms of size or strength.
Wouldn't be a bad guy to add, but unless it's a follow-up to a move for a superior talent somewhere else, I'd rather the team go after a guy who maybe has some upside, even if it's a long shot e.g. Bismack Biyombo.