Probably a step up from Polanco, both offensively and defensively. If he can emulate Murakami and Okamoto (low Ave. w/ high power output) he would be a significant upgrade at first base for the Mets.
The Mets would still need a strong right hand bat to help balance the line up. First base, DH, or LF are the best places for them to find the right-hand power bat they desperately need.