The first thing that jumps out from initial analysis is that Arias has been called a shortstop by some pundits. He’s probably not a shortstop in the major leagues. Total Zone has him as a -12 shortstop over 150 games, and that’s in Triple-A. Perhaps he can move over and play in a pinch, but the Rangers have only used him there for 32 innings in his big league career, which has spanned around 475 innings. No shortstop here.
But the Mets have a need at second base with Luis Castillo letting balls through the five hole and Ruben Tejada swinging a limp noodle, so he could still be useful at that position. And a -10 shortstop can actually still be a scratch defender at second base, so defense shouldn’t keep him off the field. His -7.7 UZR/150 only comes in 390 innings and is usually more reliable after three seasons of data – I think he can better that number with regular work.