Deribit.com is legit as long as BTCUSD and ETHUSD pairs suffice your needs.
Deribit prohibits US traders, same as Bitmex:
https://www.deribit.com/pages/docs/terms-of-serviceAny resident or citizen of the United States of America is prohibited from using the Website, holding positions or entering into contracts at Deribit.
Deribit reserves the right to immediately close any of your accounts and liquidate any open positions if it is determined that you have provided false information about your location or place of residence.
I'm pretty sure there are no legit (good liquidity) high leverage derivative exchanges for US traders. Kucoin just launched
a 20x platform called Kumex that seems to operate with the same terms (US traders allowed, no mandatory KYC) but the order books are crazy thin.