From quick Google searches, I see these model numbers under a couple of different Brand names - "Kotion Each", simply "Each" and "VersionTech" to name a few.
Realistically, they all appear to be rebadges of the same, generic (relatively) junk. Each model marketed to different users. The 9000 seems to pitch itself more for XBO/PS4 etc, the 2000 as PC.
I don't think you'll be able to quantify either as "better", but you may have some better luck with units that have been 'reviewed' to any great degree.
The 2100 unit was reviewed here: http://www.realhardwarereviews.com/each-g2100-headset/
Remember though, while reviews are worth considering - there are commonly changes in generic product lines, so there's no guarantee that any "G2100" you buy will actually have the same internals as the one reviewed almost 2 years ago.