Hi, not sure if this has been covered already, as i havent read all the posts,
but just to say that the schertler dyn-B contact mic and the PRE AI III matched pre amp is absolutely ACE. Still get feedback, but thats normal - the resonance of the bass body will always cause this at higher volumes. Need to position yourself so that you are not facing your amp.
I had a Realist for AGES, thinking it was the best on the market, but i was never really happy with the sound. Most doubles bassists are after that 'pure' acoustic tone when amplified, and the realist to me was too middy and nasal, and the output from it was far too low.
I investigated the schertler stuff and managed to get the Dyb-B and preamp all in for less than £500 on ebay. Its expensive stuff !!
Im loving the tone of it, and also the portability - it just sticks on the bass with green bluetack so moves between multiple basses with ease. It also has a phase switch to switch out the feedback if you in a cramped rehearsal space for example.
Would defo recommend. but its expensive !!
my 2c...