Blocking isn't top teir, but size helps him out. He can also hopefully be coached up a little. There's another TE, Bear Pascoe, I like as much that is a top tier blocker, but he's an RFA. Depends on the cost there...Giants really like him though.
For those who have followed Carlson more than me...how is his blocking? I remember him being very similar to Keller in being an athletic TE who never really put up huge numbers...always seemed to be on the verge, but the Jets could certainly use a boost in blocking (would prob sign off on Carlson anyway just on his pass catching ability).