Hey sorry last question, how about this phone? is this phone okay to purchase as well?
You probably won't know for sure which version you have until it's in your hands. The T-Mobile version is model IN2017, USA factory unlocked is IN2015, Verizon is IN2019, China is IN2010, India is IN2011, and IN2013 is the EU/Asia variant. This can be found in the settings menu under "About Phone".
Ideally you get the US factory unlocked version, but I don't see why a T-Mobile unlocked variant wouldn't work as well for Mint. Safest Amazon listing to me seems like this one, but choose Amazon.com under other sellers rather than the top third-party seller.
Edit: looked into it a bit, seems like some leftover bloatware on a T-Mobile unlocked model can sometimes cause issues when the phone is used on other carriers. It's possible to flash global firmware on a T-Mobile unlocked model to solve the problem (should it happen) if you're comfortable doing that.