At first, I used instances that were not very performant, causing some problems. I quickly moved to more powerful instances and since then there have been no problems at all. There is a slight delay, which is normal, since the servers are not in the same country as the users anymore, but the users haven't noticed it at all.
I can't say how well it scales, though. I have a small user-base, so scaling has not been a problem yet. Network performance might become a problem if you have a huge user-base.