I know the ali baba ... with ebikes i learn to get high quality stuff. I can’t double spend on batteries and motors, loose time and fix stuff..
Hope it will work out for you. I don’t wear helmet but for a 50mph ebike i would get a motorcycle helmet if I were you !
I love speed myself, am thinking how to get a GREYP G12H or G-12S(that is the supercar of ebikes IMO) i enjoy this wonderful ebike experiences, safety and alertness above all.