I am ecstatic about this plug-in, but probably not for the same reasons other people will be.
I won't bore you explaining why, but I need to send the OBS video and audio from my personal computer into a second computer running Zoom and other streaming apps. I do this using the HDMI output and a video capture card on the second computer.
For whatever reason, OBS, until now, would only send a "rough" audio mix out of the HDMI port and all other monitoring ports. The one critical component this mix was lacking was clean cross-fading between scenes during a transition. The "new" scene's audio would start as soon as the scene was activated, and the "old scene's audio would abruptly cut out. Given that this was the mix playing out of the HDMI port, it was the mix that my stream audience would ultimately hear - and being primarily an audio guy, I didn't want to live with that.
After weeks of tooling around, I finally came up with a workaround using NDI to send audio to the NDI Studio Monitor and then out the HDMI port. It worked, but it involved way too many apps and introduced too many potential train wrecks into the picture.
The Audio Monitor plug-in came along just in time, as I was getting nervous about doing my first "real" livestream knowing that any one of the several links in my chain could fail somewhere in the middle. Audio Monitor eliminated NDI altogether, and also relieved me of several steps I'd have to take before each stream and each time something went wrong along the way.
It's easy to get up and running and does so much more than I have asked it to do. Just remember that, depending on how you configure it and route to the various monitoring devices, you may have to mute the default monitors within OBS. If I was able to figure it all out, you'll be able to do it, too.
Good luck. I think you are going to love this plug-in!