Just looked into this lad a bit and according to Wiki
Came from Ireland to Celtic and didn't play, went on loan played a bit including Uddersfield, then went to St Mirren permanent where he played wing back/full back. Wanted a transfer in his last year was refused then left on a free to Ross County.
Won the league cup in Scotland then after contract ran out left for Plymouth where he has won POY....bit of a theme here!
Maybe he's a late bloomer, maybe having been played defensively early in his career slowed his progress. But he has done well for Plymouth, and if he's a free transfer I can't see him being a costly risk.
He's left footed, where we have Stevens, Lafferty at the moment and played wide left and attacking midfield for Plymouth.
If this is a goer, I can see him as a cog....part of the squad brought in for specific roles and tactics and if he has the guts and determination to make the most of his talents then who knows, He could be another gem.
But it is concerning that there has never really been any clamour for his services, and though I know I haven't been watching there doesn't appear to be a lot of news now either.