I think Yacob is a limited footballer but in certain games can do an excellent job.
Against Arsenal i thought he was brilliant, most teams have more possession than us but teams such as Arsenal who are a quite patient and knock it around a lot, Yacob is good because he gets in their faces and breaks up the play and protects the back 4.
The reality is though, if a team can find a way past that, he offers us little else, he cant change his game, its just the way he plays. When we played Palace, Leicester and West Ham this season (those spring to mind) he has struggled because they attack at pace and dont give him chance to break the play up.
To me i think we badly need an alternate option in January, play Yacob against the likes to Arsenal, Man City, Bournemouth, Swansea (there are others but they stick out as the keep ball teams) and games where teams are more direct or counter attacking, leave him out.