BaseFEX:
The chart and the order book is not as good as Deribit and Bybit but seems, like someone said, still acceptable.
Bitmax and a few others:
I need an American-friendly exchange that offers altcoin pairs and high leverages. So I didnt bother.
It doesn't seem like BaseFEX is US-friendly either. They might allow US-based IP addresses but this is posted on their registration page:
Currently, BaseFEX does not support users from following regions: United States, Cuba, Iran, North Korea, Sudan, Syria, China, and Crimea.
Back to square one?
Volume on Kumex's XBTUSDM contract isn't great yet, and I think that's their only market for now after launching a few weeks ago. They appear to allow US residents.