overly 'smoothing'/'rounding' effect on the sound
This is the effect I get with Filter engaged. Going back to AP I get more treble detail(especially cymbals) and bass, all round better sound. Moving from 120 SFS to 4 SFS is better and easier to hear. This is without the NOS.
Longer digital cables(over 1 metre) have often been quoted as sounding better going back 30 years.
I think Intona(and other devices) are very system dependant but I think it also has a similar effect as quoted above. Unfortunately it improves some aspects of the sound so I have it in my system. It comes down to your own audio morals whether you can live with it or without.
Robert