As JBA said, the problem with any player is that, in January, they need to be able to immediately fit into the system. Otherwise they are better off being summer signings with a full pre-season.
Does Furlong fit into that category? I remember him bombing up the wing, but under Kettlewell he certainly wasn't coached to play all the short passes across the penalty box, or to find a man rather than punt a clearance.
As the manager said, however, clubs don't just start looking for players during the window. It's a 365 days a year process. So if we didn't bring in a new left back it's either because we couldn't find one that was ready and available, or that JBA didn't think we needed one at this point.