Hey @funkytwig, I've disabled Sogo Connector and set up Cardbook, and Cardbook is working perfectly
I'm connected to Nextcloud rather than ownCloud, but it should work just fine for you, too.
The first run wants to import your contacts from your existing Thunderbird addressbooks. I did this, but later deleted them from Cardbook (they're static, not synchronised). I even deleted my existing (Sogo sync'd) addressbooks to ensure I was only using whatever Cardbook provided. I created a new Cardbook remote addressbook using the link provided under "ShowURL" in Contacts in Next/ownCloud.
It synchronised way quicker than Sogo Connector ever did, and better yet, it sync'd all the email addresses for a contact, not just the first two! You also have extra options about sorting and displaying contacts that you don't have via Sogo sync'd addressbooks. Actually, I think the Thunderbird devs should incorporate Cardbook by default (like they do with Lightning). Cardbook is a way better addressbook system, way better than the limited 90's style addressbooks Thunderbird has now.
Calendars are still just fine, syncing via Lightning.
There were a few reviews in Cardbooks addons page that were quite critical, claiming it doesn't work. I get the impression there was a bug in a previous version (possibly 21.5), but the current version is 21.8 and it's working perfectly with Thunderbird 52.2.1.
I hope this helps, and gives you the confidence to try it out.
Good luck, Ben!