I've tried Amazon affiliates for non-US countries on some YouTube video and it was a bit of a pain in the ***.
Firstly you have to create separate accounts for every Amazon Affiliate country. Not to mention that Japanese signup form is only in Japanese and no English. Also, the payments are being processed by every Affiliate country separately.
Then when it comes to linking, if you have a website, you can install the plugin that will apparently send your user to the localized website according to his country of origin. Well, no such thing for YouTube videos, so we did
"US: link
UK: link
DE:link" and so on for our 3-5 most common GEOs.
I guess the conversion rate for non-US/UK countries was a bit lower, mostly due to the fact people don't use Amazon so much to buy things.
For all the other metrics, i can't really say much, since we didn't have enough traffic to draw any actual conclusions from it.