I measured it with a calibrated sound meter, and it attenuates my sax playing from 105dB to 79dB. Its barely audible in the next room now.
Its quite comfortable, but heavy. I would recommend to lay it on a chair in front of you and play like this, or Your back will be killing you
Low notes from low D down come out a little harder than without it, but rest is the same.
You need to play with the headphones or it doesn't sound good.
Include mic sounds quite good actually.
Also You need to take brakes every 30min to vent it or inside gest very wet and damp.
I would recommend it.