I think this was another good signing by Shero (looking over the totality of things the last few years). It might be a little tough to swallow in that last year if he's slowing down or out for a large number of games, but he could've asked for more money and gotten it, so you give an extra year on term and hope for the best. I think he'll be fine.
I'd rather see Kunitz get this type of deal before Iggy because he's less of a risk IMO. We're going to need some reliable veteran guys the next couple seasons potentially if we go young / cut a bunch of veterans loose. Among the veterans, he, Cooke and Dupuis are the three I'd want to see stay. Or any two of those three if that's what it comes to in order to keep Letang.
He's also the only guy who has proven he can be a big part of both Sid and Geno's lines, whereas Dupuis has never done well with Malkin and Neal in his limited time with Sid, was not great (and I think would not be great generally because of their playing styles as compared to Neal with Malkin). Hopefully Bennett will be the next piece that meshes well with both centers, when asked. That's one thing about Boston: those top six guys can be mixed in several different ways and it usually works.