Doing that requires transcoding and generally has very bad performance for me, this doesn't look like it does that (but I haven't tried it yet).

Casting a chrome tab typically means re-encoding your screen frame buffer, sending it to chromecast and decoding it there. Whereas this app merely pulls the video off the URL and decodes it in the chromecast. Your system has no load and it can even be turned off when the video is still playing back (although you'll have no way to control it).

Looks like its streaming arbitrary video URI's without needing to fullscreen the tab

When I do that chrome-tab-cast, the performance is terrible.