They do update the firmware, but it does lag behind the official updates quite a bit. I also don't think that the 3.0 on Kon-tiki directly corresponds to Onyx's official 3.0. I've been following the discussions about Kon-tiki on Russian forums, as I have a Nova 3 and it's pretty much the same hardware (only with the Wacom layer and newer firmware).
I would get a Nova 3, as the screen seems clearer than on the Nova Air. This is if you really want or need the features of the latest software. Otherwise I would probably keep the device.
EDIT: I just remembered: the software for at least the Russian Kon-tiki doesn't update over the air. You'd have to manually download and install the update. So there might be updated firmware for it already. But you would have to find it on their website.
The latest firmware can be found here:
https://onyxboox.com/support/boox_kontiki2
It might be that you are already using the latest firmware, since you bought the device recently.