I switched to CloudKit from Dropbox. It works fast and no issues yet. When I say fast, it seems faster to me. I don’t have an objective measure on that.
My reason for switching:
An odd error would creep in from DB stopping sync. According to Jim in DT support there is a difficult error in DB affecting some DB & DT users. DT is continuing to attempt workarounds but has not been successful yet.
My DT databases would not reliably sync on DB. They might work for a season, then stop. I would then clean the store or create a new sync store then start over. Things would be fine for a season, then stop. I even tried multiple sync stores spreading the sync load and again, it would work for a season then stop.
When CloudKit became available, I tried it since the most recent updates to DTTG and DT stopped my DB sync again.
My problem was somewhat complicated by the Ghost files DTTG 3.x created upon conversion. These also stopped my sync, even with CloudKit.
Once free of Ghosts, CloudKit has worked very well. It is important you sync only one DB at a time as suggested in the forum (Note from Jim). CloudKit will throttle your efforts if you try all your DBs at once.
I have one DB that would not sync with CloudKit. I have a 72 GB database with 852 scanned books. A few years ago I scanned all of the books in my library. They are now all searchable in DT. This process is a subject for another story. While CloudKit would stall syncing this to my iPad, I was able sync on DB (go figure). I give this database its own sync store. We will see if this sync will stall like the rest but for now it works. It is fun having my library available on my iPad.
One additional note. All my DBs are indexed. The files live on my iMac but the folders are also synced to my DB account. I had several reasons for indexing. One of the reasons for my shift to indexing was to remedy the issues I was having with the DB sync. Like all my other efforts, sync worked for a season, then stopped.
I hope my story helps you in your evaluation of CloudKit. I had great help from Jim with DT support in understanding the issue with DB. He also gave me advice on sync with CloudKit.