I am working on building a live streaming system for my church and have settled on using PTZOptics cameras for the project. Our AV dealer wanted to set them up with SDI connections and then go through a capture device. For cost reasons I am looking at using the IP video capabilities of these cameras instead. We are currently using OBS to combine the sound from our mixer with the feed from a webcam before sending it to Facebook. As I've looked over the options from PTZOptics I have a question about the advantages/disadvantages of using NDI over RTSP/RTMP? The closest I've come to an actual comparison is a PDF of talking point slides that simply said "NDI evil" - not very helpful.
We used RTSP and it works fine. There are a few benefits of NDI (like doing PTZ controls over that protocol) but not worth the price jump for the cameras, in my opinion ($600 to upgrade each camera to NDI).
We do notice a ~200 ms delay in the video reaching the mixing PC behind the audio so we just use Vmix to delay the sound and match them up.