Warning:
I tried a WH4 remote i bought in 2021 from Firduo.
It has a signal jump issue and throws in power jumps at certain throttle positions where the communication faults. This makes it totally unrideable and unsafe.
A company that fails to fix an issue like this before selling to customers should get sued for all they’ve got. 
I think newer WH4 remotes sold by the larger companies have a later revision which has fixed this issue but beware: don’t buy it from unknown resellers on alibaba, aliexpress, banggood or ebay which might sell the old design with this issue.