The downside is that I sometimes have to enter the master password on my phone's on-screen keyboard, so it is probably shorter than it should be.
I very much want to find an alternate sync solution. I think it is kind of pointless to have a secure password solution if the underlying sync is insecure or more accurately has a dismal approach to security.
The only thing I'm a bit worried about is accidentally deleting or corrupting the password file, as Dropbox could then synchronize this change across all devices. I guess I should back it up regularly to non-Dropbox folders to avoid losing all my passwords.
But it's the best I have found to get folder-sync for sensitive stuff (my notes folder) without relying on a 3rd party for storage or security.