Citation exports are not always accurate.
The browser plug-in does not offer a way to log out. This is a problem if you use a shared computer and don't want people to be able to access your log-in information and/or see what you have added to your libraries. The plug-in is really handy when used on your own personal computer, but I do not recommend syncing the browser plug-in with your account on any shared computer in a computer lab or a laptop checked out from the library.
There are some known issues with some databases. See list of known problems from Zotero.