Why do you need it ?
if your rear light has three cables, but it can't work in Ubox V2's lights port, then you need this converter.
it will keep your head light on, and also keeps rear light weakly on, and when braking, it will light stronger.
Is it compatible with other VESC?
It's only compatible with Dual Ubox v2 75V and Ubox V2 100V