It's a bit larger then most groupware. It's more of an entire Google Workspace replacement. Installing and running it can also be a bit more of daunting task. We ran it for 10+ years on premise before we migrated to Google Workspace.
I think most people can safely rule-out Open-Xchange unless they've got deep pockets.
Sadly commercialism has taken over there, and their sticky hands have now reached Dovecot.
The open-source version of Dovecot 3 will have the vast majority of multi-server functionality stripped from it. OX have stated on record[1] that their plan is that open-source Dovecot 3 will supported and maintained for single-server use only. If you want multi-server you will need to pay $$$$$$$$$ for the commercial version.
You mean a GMail replacement? It does not look like it does anything other than email, which is only one piece of Workspace.
I remember it having chat and calling capabilities too, but on github their messenger is marked as archived and the mobile app seems to have been taken down, so I'm not so sure about that.
Maintaining OX is not super much work but it is a complex piece of software. You'll have a lot of moving parts; Open-Xchange (OSGi / Jetty application), MySQL, Postfix, Dovecot, etc. All these parts need monitoring, disaster recovery, high availabilty setup in some cases, etc.
The "absolute amount of time" these things cost isn't even super much. Especially if you are already pretty proficient in the technologies. But, personally, the hardest part of maintaining a bunch of these opensource solutions on-prem is that you are people's "go to person" for it. Meaning everything what happens to it is "your problem". For example if people perceive the solution as slow, you will need to deep dive in it. If Google Workspace is slow it's a Google problem. Maintaining these solutions (at the time we also used Zulip on-prem, Asterisk and some other stuff) becomes a recurring distraction. Patching, investigating stuff like a failed backup, breaking updates, testing updates, user complaints, etc.
So for us (about 60 people at the time) it simply wasn't worth the effort anymore anno 2018 to self-host it if you could offload it for 15 Euro a month to Google. But when we started out in 2005, it was. Also keep in mind that in my role as software developer the on-prem stuff was a "secondary objective".