That counts only Russian, Western Europe, Eastern Europe and Germany to USA and lately region restriciton was lifted for most of DI/DIR keys so it's worth a try. I redeemed many of the NA keys without need of any fake ISP/VPN so this is example with FME.
A small correction. You are linking us the app, not the sub. Amazon is selling keys, so it should be sub 15204
. You'll notice the "billingtype: Proof of Prepurchase Only", aka key, as well as the list of countries that cannot purchase this serial.
As for what can and can't be redeemed, my XCOM:EU is the russian version, and I did play it without needing a VPN after the first 12 hours or so. It is currently impossible to redeem the game though, since the sub has changed. But the app id is still the same.
And yes, I did forget a few more regions, including Germany, Australia, Japan and China, and quite probably a few more.
Additional info. Only region locked "Front Mission Evolved" retail key is the Japanese one. Would a screenshot of me having redeemed a Russian FMT say anything about the rest of the RU keys? So it remains a game by game case for whether NA keys are region locked or not, no matter what our previous experiences with them were :(