I don’t use either (both? – it?) but am curious at the distinction between facebook-chat:
Facebook chat is the instant chat messaging system by Facebook.
The instant messaging service, once "Facebook Chat", that includes transfer of audio and video content. It is distinct from the main Facebook app, for which there are several tags, including facebook-messages with which this should not be confused.
Is it really only whether or not on a hand-held device and if so is that made clear enough (if necessary)?