KVR Audio

as far as I can judge, both of these plugins are supposed to have a similar use in mixing/mastering

Apart from the enormous difference of price between the two plugins, I'd like to know more about apUnmask under the hood, if you'd agree ?

apUnmask does exactly what's described on the webpage. It is in fact quite simple. It takes the incoming signal, feeds it through the Opus codec detection algorithm, but instead of removing the data deemed to be inaudible like Opus, it allows you to boost those parts - controlled by a linear phase graphical equalizer, to enable control over what gets boosted. Just download the demo and try.

Sounds quite interesting... gotta try