There have been plenty of decent 'keepers come over from the MLS; I'd also add that given the skillet required of a GK are so different to that of outfield players that the level of league you play in is arguably less indicative of your capabilities it is for outfield players. Happy to be proven wrong though by someone who is more knowledgeable than me in goalkeeping.
He's also the US #1 ahead of City's #2 GK.
Appreciate there is a degree of risk with this signing, I'm just not convinced it's a high as some are making out.