Goalkeeping in a league-chasing team is an odd one. It seems that perfectly good keepers can look poor based upon one error in a match or even 1 error in 3 games.
However, keepers playing in mid-table or relegation teams often look amazing because they save 6 or 7 attempts at goal yet still make that one basic error. Perception gets warped slightly.
David James and Brad Fridel spring to mind of keepers who were branded as shocking keepers but are now two of the best in their twilight years playing for smaller teams.
What I'm saying is Hart is probably the same. He looks great diving left, right and centre when under pressure for Birmingham but he'll probably look weaker playing in a team challenging for the title as he'll make one or two basic errors. Same could be applied to Shay too.