Can I use this completely isolated and offline, or does it require you to use it online or is otherwise severely limited if you don't? And it is easy to get it in this mode in a clear way? Their website doesn't make this clear if this is possible.
Yes, by default it is completely offline. You have to take extra steps to connect it to any kind of online service, such as a Zotero web account, or Dropbox for file syncing.
It is completely isolated, if for example you want to include references in word. However some functions like adding references quickly with DOIs will fail without an internet connection.
