The former Swansea City midfielder has joined Bolton on a Bosman.
"He has got fantastic energy, maybe more of a box-to-box player than Bolton have got at the moment, and he's a big lad too," Darby told the Bolton News.
"He didn't get many goals last season but he has got that in his locker, as he showed in the play-offs.
"I know it was in the last minute, and that our keeper was in the opposition penalty box, but it still takes some player to do what he did. He showed that composure and he'll need to do that a lot in the Premier League because it will be faster than anything he'll be used to."