Thank you all for the replies!
ome may be thinking about their answer to this question. But I think nobody will tell you in writing to install OMV6 in a case like this ... What would you say if someone asked you this?
I would never put beta software in a Production environment for a business.
In general I'd agree that for production one should always go with stable.
That said, I've recently installed Debian testing (bullseye) in a production server. That was just shortly before it became stable. It had been in freeze for several month and I went through the Release-Critical bugs that were holding back the stable release and none was relevant for my intended setup, so I felt confident to install a "testing" release. That saved me from upgrading it a month later and provided a newer PHP version, which I needed.
I don't regret that decision.
In that particular case I knew where to look for RC bugs and what to expect. When it comes to OMV, I'm not so sure... I had a look at open issues with OMV6 tag in OMV's github and I didn't see anything that would particularly raise a red flag for me, but I'm not so familiar with OMV, nor so sure that's the right place to look for this kind of info and if the issues reported there tell the whole story... that's why I asked...
Perhaps my question should have been... What RC bugs are holding OMV6 back from being released as stable?
And my other doubt is... Is upgrading OMV to a new major version as smooth as upgrading (vanilla) Debian?