I mostly eschew tweaks and like so many find snake oil afoot. However, when it works it works and in a very deliberate non-argumentative way.
When I installed a Decware ZLC conditioner, the POSITIVE effect was immediate; blacker background, greater separation of instruments and vocals. It is a subtraction device. Subtracting whatever seemed not there, but clearly was.
I sent one to a friend and he confirmed same findings, the effects as dramatic for him. We laughed at the craziness of electricity and the hobby.