Totally agree with this. Doesn't matter how good someone is at another club, a transfer is always a gamble, just because they perform well at one club doesn't guarantee that they will maintain that standard at their new club. IMO, players are like plants, just because they flourish in one part of the garden, doesn't mean they will grow as well if you uproot them and plant them somewhere else.
Our best bet is to try and unearth an unknown a la Harry, but the chances of that happening again so soon is pretty unlikely.