Ihedigbo joins the Lions after spending two years with the Baltimore Ravens. Current Lions defensive coordinator Teryl Austin was the Ravens' secondary coach during that time, so there's already a pretty good amount of familiarity there with Ihedigbo.
In Baltimore, Ihedigbo started all 16 games last season. He recorded 101 tackles, 11 passes defended, 3 interceptions and 2 forced fumbles. He started only 3 games in 2012, but he was a starter for 12 games with the New England Patriots in 2011. Before that, he was more of a role player and a special teams guy from 2008-10 with the New York Jets.
Ihedigbo was ranked as the 16th overall safety on Pro Football Focus last season. He was quite bad in coverage (73rd in that category) but quite excellent in stopping the run (second behind only T.J. Ward). He also did quite well as a blitzer, coming in one spot behind new teammate Glover Quin. Considering Quin ranked 10th in coverage among safeties last season, and considering the Lions are moving back to free and strong designations, Ihedigbo projects to be the team's starting strong safety. Quin will likely move into the free safety role since he's much better in coverage.
While it would have been nice for the Lions to add a top safety like Ward or Jairus Byrd, signing Ihedigbo didn't cost nearly as much. There's a reason for that, of course -- Ihedigbo is already 30 and isn't a top-tier safety like those two guys. However, Ihedigbo's familiarity with Austin and his ability to mentor the Lions' younger defensive backs make him a solid option. This isn't a long-term fix at safety by any means, but the starting safety spots now appear to be set for 2014.