Klavan is decent. He's obv not a first choice but he's experienced, was cheap and seems happy to be back up for us. Also being left footed offers that bit more variety in CB. MY only problem is he needs to be about 6 inches taller because although decent in the air, he's bit of a short ass defender so gets beaten by any taller striker.
Like Sky said, there aren't many 4th choice CB's out there who are better than him?
City - Kompany, Laporte, Otamendi, Stones
United - Baily, Smalling, Jones, Rojo
Chelsea - Rudiger, Luiz, Cristensen, Cahill
Arsenal - Mustafi, Kos, Holding, Chambers
Stones has potential even though hasn't shown in, but wouldn't put him behind any of the other 3 4th choice CB's in that list (No idea on united 4th, but Smalling/Jones/Rojo all as bad as each other really).