Their support for ONVIF is, as you said, limited. Being able to add a camera into your protect feed is a good start, but until they make it work better for PTZ, audio, sub stream capture, and everything else it’s not worth note IMO.

RTSP allows you to check a live feed in another software suite (even just VLC) but again, without the cameras themselves being ONVIF standard you’re missing all the aforementioned features and now you’re really REALLY overpaying for what is essentially a dumb camera.