There are a number of reasons to be leery here. Martin's batting average last season was just .211, and while there's reason to expect that to bounce back a little in 2013 (his batting average on balls in play was very low), he probably won't ever again hit for average like he did early in his career. Also, the move from Yankee Stadium to homer-suppressing PNC Park won't be an easy one for him, especially since he's right-handed.
The problem is that is that you'd prefer not to have to turn to the free agent market for a catcher. Or any player, really, but especially not a catcher. Free agents are old. As a group, they're in decline. Catchers, in particular, decline at a very early age. If Tony Sanchez had turned out to be as good as the Pirates hoped when they drafted him No. 4 overall in 2009, or if the previous administration hadn't passed on Matt Wieters in 2007, the Pirates wouldn't have needed Martin, and everyone would have been happier.
Unfortunately, the Pirates needed a catcher this offseason. The list of free agent catchers was not a good one. There were some trade options they could have pursued for unproven catchers like the Angels' Hank Conger. But those options weren't sure bets either. Given that the Pirates were going to enter the free agent market for a catcher, they did well to get Martin, despite his obvious flaws. He's younger than most free agent catchers (he'll be 30 in February), he's a better hitter than most of them, and his defensive reputation is excellent. He won't single-handedly fix the Pirates' notorious problems holding runners, because the Pirates simply don't prioritize the prevention of basestealing. But his work with the glove should be a big plus.
At two years and $17 million, the Pirates paid a fair price. There were reports indicating they could have signed Martin for three years and $25 million, which would have been worse, even though the cost per year would have been marginally lower. The Bucs will now hope Martin doesn't decline too rapidly before the end of the 2014 season. If he does, they could be looking at another Clint Barmes -- Barmes was signed to a two-year contract last offseason, and most fans came to see that deal as an albatross as Barmes failed to hit. But while Barmes wasn't exactly good, he added a lot of value with the glove that most fans missed.
Still, the Pirates will hope for something better than that. If Martin can bump his average up to .240 or so while still providing walks and 15 homers or so, he'll earn his money. That wouldn't be particularly inspiring, true. But it would beat what most of the other free-agent options would have provided. Between Martin and Michael McKenry, the Pirates are more or less set at catcher for the next couple years. I'm not thrilled about the Martin deal, but it could have been a lot worse.