In general; you get what you pay for. The batteries of the "cheap" e-bikes are low grade. Same goes for the other components. If I was you; I would rather go for a good condition used e-bike rather than a new "nonbrand" bike from China.
I could be wrong, but it seems to me that importers look to Alibaba,com for a lot of 20-100 bikes, while a single buyer would look at aliexpress.com for 1 bike.. I have bought an ebike motor kit off aliexpress and was happy with the price, quick shipping, and quality but I knew who made the motor, and to some extent I knew that the company selling it to me had been around for a few years.
For a complete bike, there are attractive prices on aliexpress, but more things can go wrong especially as these are all brands you never heard of. So if I wanted a bike, there are reputable retailers in the USA who sell online, with good pricing on domestic well known name brand product and reasonable shipping fees. In short, I think low price is not a good enough reason to pick a chinese brand.
In reality, probably all the ebikes are made in China anyway, just like laptops, phones, and cameras, but the better known bike companies pick and choose components that are better quality.