I just used Plasma One to try a purchase with it, and the rewards are exactly the same as Etherfi’s—there’s absolutely no difference.

That is to say, Plasma One and Etherfi have the same cashback and the same cards.
They’re used completely the same way.
However, Etherfi’s cashback is credited right after you spend, while Plasma seems to take about a week to withdraw.
But Plasma One only requires a Chinese passport plus an overseas address to apply, while Etherfi seems to be quite troublesome for Chinese users to set up.