It's illegal for him as a USA citizen to buy these kind of assets, the only thing Stox get get him is a shit ton of trouble.

13.16    you are not a citizen of or resident or domiciled in the United States of America or
making a contribution for the purchase of Tokens from a location in the United States of
America, nor are you an entity (including but not limited to any company or partnership)
incorporated, established or registered in or under the laws of the United States of
America, nor are you making a contribution for the purchase of Tokens for or on behalf
of any such person or entity;

https://www.stox.com/assets/contribution-terms.pdf