If you are buying this to connect a webcam or another camera for live streaming via HDMI to the computer (like I did), this is not a good option. The delay is unacceptable, even with very short-run cables (under 1m).
I didn't try with SDI because I don't have such a camera.
Also, don't even think that USB-C cable is the same as Thunderbolt. It will not be accepted (especially by the Mac OS) and the Recorder is not detected.