He has been in another country and another league his entire life, and probably doesn't speak a word of English (which is vital for communication with defenders, right?). It would take him at least a year to get used to the pace of the premier league (a lot less build-up, a lot less tactics, and a lot more lumping the ball forward/relying on deadball situations). Plus he has to get on the same wavelength as the back 4, which will also take a while.
That's what I meant in that he won't be an improvement over Fabianski and Vito. Both of them have been with Arsenal for almost their entire careers and know the club inside out. We honestly don't need another year of transition, and where every point counts, if we really have to get a new keeper I hope it's someone from the premier league like Al Habsi or Vorm.