This is their official website.
That is YLMChina/Coolbaby's official, english-facing website.
As far as I know, they manufacture a bunch of the current cheap handhelds available, but not necessarily all of them. Their official website doesn't seem to sell direct to consumers, and doesn't even list all the products they actually manufacture and sell, anyways. See https://nds-gba.en.alibaba.com/
for what seems to be a more useful, updated list.
Do we have confirmation that the RG350 is a YLMChina product? @tonyjih
, are you and the RG350 project affiliated with YLM?