Agree that iCloud sync in DEVONthink is slow at best, unreliable at worst.
That broke my heart a bit, as I’m drawn to DEVONthink (and have used it successfully to organize large projects, like a book on Celtic folklore). I love the See Also feature, which I believe is the most powerful feature DEVONthink brings to the table. And results I got when using DEVONthink to analyze years of dream journal entries blew me away. (There’s a related post on my personal site, if folks are interested.)
But, I really don’t care for the gray, utilitarian, multi-pane environment … and, in the end, the unreliable syncing and the lack of a useful iOS app were deal killers for me.