Yesterday I tested the MFB VCO and the MFB Dual ADSR with my Roland System100 mod 102, during the test I did some demo recordings.
The demos are quite long and in every demo I used the same “sequence” and tweaked the knobs to let you hear the behaviour of the system.
As the melody is quite redundant  I hope you don’t get annoyed and focalize your attenction on the sounds.

• VCO MFB with Roland filter
  The MFB VCO (only one vco) passes trhu the Roland System100  filter.
  First I use a saw wave then a square without any modulation and play with the filter to show as the the two modules interact.
  

• VCO MFB with System100 and MFB Dual ADSR
  The MFB VCO pass thru the Roland filter and the MFB env modulates the Roland filter cutoff.
  It starsts with a saw wave , than at 1’30 I switch to the PWM and continue playing with the filter and with the MFB env.
  At 4’50 I turn the Roland VCO volume up…
  

• VCO PWM (Roland System100 vs MFB)
  Here’s a comparison between the two vco passing thru the Roland System100.
  They both produce the PWM with a similar rate, the MFB sounds a bit harder, it may need an attenuator for PW mod…
  The first is the Roland and the second is the MFB

• VCO SAW (MFB vs Roland System100)
  Here’s the comparison between the two saw, the first is the MFB the second is the Roland

PAY ATTENCTION!!
When you listen to the sound keep the volume at a fixed level, don’t turn up the volume when some sounds seem more quiet because there are some resonance peaks that can DAMAGE your speakers and your EARS!