Sure, I've used it many times. It really reduces the sound output sound and allows me to play my system 24X7 in order to decrease the break-in time required for my new speaker purchases. I sometime also cover the face to face speaker pair with blankets to further reduce the sound output.
I agree that caution is necessary because the sound is greatly reduced by cancellation and you could drive you amp into clipping or overdrive the speakers without knowing it. It's best to first play your system in a regular layout to determine what position on the volume control is moderately loud before doing the cancellation setup. Never exceed the volume control level that you previously determined was loud in a normal setup.
TIC
I agree that caution is necessary because the sound is greatly reduced by cancellation and you could drive you amp into clipping or overdrive the speakers without knowing it. It's best to first play your system in a regular layout to determine what position on the volume control is moderately loud before doing the cancellation setup. Never exceed the volume control level that you previously determined was loud in a normal setup.
TIC