Let's play a game called "Spot Sooki". One of these nails is painted with Sooki, the others with America.
Can you tell which one is Sooki? It's the ring finger. Yeah, I can barely tell a difference either, except Sooki is every so slightly darker than America. If you were a neurotically season-conscious polish-wearer, I would use America in the summer and Sooki in the winter, but it's not like anyone would care if you didn't.
So, should you buy both? No, but if you already have one of the two and it's running on empty and you can get the other as a freebie, it's a good replacement option.