The original basic principle of simple 'feedback destroyers' was to have a number of manually tuned filters of extremely sharp notch type attenuation filters, which were tweaked to depress the amplification level at the frequencies needed.

Nowadays you can have 'semi-automatic' ones which have small computers on board, such as PICs, which detect when a particular frequency range is suddenly peaking, and act to cut it back. This may mean that the operator is tempted to 'ride the gain' on the whole amplification chain to a higher level than with the manual ones, leading to the 'muddying of the highs and lows' syndrome.

I have no idea of the internal technicalities of the Behringer, or any other.