There was a complaint in this thread that it isn't peer-to-peer, which is...kinda weird. Requiring that your recipient have the device they want to receive it on running at this very moment is kinda a non-starter for a file sharing tool, IMHO. Doing that without it being a Mozilla-hosted app isn't really a thing I'd care about. P2P is neat, but it's not a very good user experience, especially for non-technical users.