I go home and my laptop is smart syncing the recently active sessions only which conserves space on the laptop drive but lets me do some small work on recently active sessions.
It's totally seamless and I cannot recall the last time I was even alerted by Dropbox about anything except that I was hitting my 3TB cap soon.
The only issue I ever had was using it on Windows where it would occasionally create conflicted file copies, which was annoying, but moving to OSX resolved that.
I use Nextcloud and there are parts of the UI that defy logic. For example, when I select a file it brings up an "Actions" menu that's hidden via a hamburger button. It has 4 options and I have about 3000px of horizontal whitespace on the same row.
TLDR; It's all hamburgers and whitespace and I don't understand why.
There are at least two big variables here:
1 - Is the new UI actually better? by how much?
2 - What's the cost of change for the existing users?
Bonus complexity: There are large groups of different customers inside your customer base.
If your product is the best ever with no competitor in sight you can annoy them almost indefinitely, the second anything remotely similar appears, all the built up resentment just fuels the migration and it usually behaves like a tsunami, at first it's barely noticeable until a 3 foot wall keeps going and going and you can't do anything about it.
If I'm downloading something from a Dropbox, that's a pretty good sign I'm not going to be working with that person much, or it's a one-off task.