I haven't used this but from their website / description it looks like they are more of a on-demand file transfer service, e.g. they are comparing themselves to Magic Wormhole, PairDrop, LocalSend, etc.

Syncthing has its roots in being used for automatic file/folder synchronization, that's its strength. But sure, you could set it up for a one-time file transfer too if the other person is willing to set up Syncthing on their end.

DashBeam does seem to be able to do transfers via web browser, that could be an advantage if the person you want to transfer something to/from does not want to install anything extra on their device.. but I don't know how well any of that works in practice.