I specifically purchased this add-on to create backups to Dropbox, which this plugin does not do. At least for Xenforo 2.0 (not sure about the 2.1 version of the plugin)
This was not stated anywhere in the listing. My only options are local, FTP, or Amazon S3.
Only workaround is to create them locally and then upload them to my Dropbox...not really what I was looking for but as a backup creation tool it does work. 2/5 because it does not do what it advertised and what I purchased it for.