Childers saw an increase in swinging strikes last season for the Charlotte Knights. Perhaps he changed his delivery or developed a new pitch, but Childers' SwStr% went from 11.2% in 2007 to 16.9%, he also threw less balls. Childers' primarily uses his mid-80's fastball, change-up, and an assortment of breaking stuff.
If you recall, Childers spent some time with the Rays in 2006. He only lasted 162 pitches, and roughly 43% of them were balls, yet Childers still got 8% swinging strikes. Childers gets a ton of groundballs, well over 50% the last three seasons. It's worth noting that Childer's BABIP was 0.367 during his Rays time, and while he didn't help matters with a 4.70 BB/9.
He's probably a 4-4.5ish FIP reliever capable of getting groundballs. That's valuable, and for next to nothing, it's a good signing. Even if Childers doesn't see the majors.