They have a ridiculously cheap lifetime deal atm and everything is GPL.
Currently they only support ACF and Toolset integrations. I've contacted the devs about Meta Box but they're deciding on features based on github requests. So please upvote / comment on the github issue at the of this post to help make this happen.
Even if you don't plan on using Oxygen, integration = more exposure for Meta Box which is good for the whole community.
Anh, would you consider pinning this post for a few weeks?