Boyue does have a
website. It's in Chinese, though!
There are rumors that Boyue has an Android 8.0 upgrade for at least some of their devices in the works. Just rumors as far as I can see; no official statement yet.
I own both devices. The Mars has the SD card, and Boyue has offered more firmware updates this past year than Onyx has for the Nova. But comparing the two devices in every other way, I like the Nova better. The Nova edges out the Mars in overall performance. Quickness, smoothness, the frontlight, the native reader app, to name a few. I use my Nova much more than my Mars. Others may score it differently, but the Nova is the better device - unless you need the additional storage that the SD card provides.