Atchison, 37, pitched for the Mets in 2013, throwing 45.1 innings with a 4.37 ERA. Here are some other figures from recent years:
Provided by Baseball-Reference.com
As you can see, he was very effective in 2012 with the Red Sox, so I suppose there's some upside to him, but pitchers his age are rarely improving, and a relief pitcher on a minor-league deal is not someone you should get too worked up about. According to pitchF/X data, Atchison throws a 90-91 MPH fastball, along with a slider (possibly a cutter), curveball, and changeup.
No harm in signing guys to minor-league deals.