The JJ ECC83-MG is a fine sounding tube. I was unable to notice a loudness reduction compared to the standard JJ ECC83S tube. The tonal characteristics were easier to hear. Compared to the JJ ECC83-S this tube sounds a little more eager to hit the midrange. I’m not sure how that will work in all audio applications, but in a guitar amp it’s great. It can take a bit of wooliness out of a standard Fender tone stack by taming the bass response.
Bottom end is ample but not enhanced. The smaller plate structure helps keep microphonics under control, making it great for combo amps. The way it sounds makes me think it will be a winner in Marshalls when replacing the Chinese tubes people like to run. Boogies will boogie and Fenders will be fine. If you are looking for some affordable experimentation, this should be on your short list.