NDI vs RTSP/RTMP in PTZOptics cameras
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.