I've just had the Invidia Gemini with Berk HFC's fitted to my 350, and am totally over the moon with it. Was on the motorway last weekend and totally no drone at all, just nice silence.....unless you hit the loud pedal.
All round it has a lovely tone whether it be on tick over or giving it full beans........but definitely no drone!!
+1.
Love my Invidia Gemini system with Berks HFC's.
Absolutely no drone from what I can tell at all ~ drove it yesterday for around 40+ miles at various speeds/rpms up & down the M4 with no unwelcome noises.
Just a great sounding combo.