The Red Sox had what might be called a subdued offseason, but that doesn't mean they were completely inactive. And while most will focus on A.J. Pierzynski and, more recently, Grady Sizemore, the team's biggest new signing in terms of dollars was actually the under-the-radar (it's not even on the Wikipedia page at the time of this writing!) acquisition of former closer Edward Mujica on a two-year, $9.5 million deal.
So why is Mujica overlooked? There's really no good answer for that beyond "he's a bullpen arm". The last three years have seen him produce better than 200 innings of sub-3.00 ERA baseball. His strikeout rate over that period wasn't fantastic, at 6.8 per nine innings, but his walk rate is almost Ueharan at 1.4 per nine.
In fact, Uehara has to be the go-to name for comparison here. Better than half of Mujica's pitches in 2014, after all, were of the Splitter variety. That's more than any other pitcher in the majors, with none other than Koji himself coming in second at 48.3%.
If there's any real cause for concern, it's that Mujica hasn't pitched in the American League since the first (ugly) years of his career, and that he faded in the last month of 2013. But are you going to let that get you down?