I have tried the MB Super Synth, the Octavius Squeezer, EHX MicroSynth and the Future Impact.
The Super Synth sounds great but tracking leave a bit to desire for my playing style. The Microsynth is basic, I had it twice and got bored twice. The Octavius Squeezer is my fav pedal but not so much for pitch tracking Bass. I love it for it's amazing filter and envelop and fuzz (it contains my favorite envelope follower). The OS can get some nice acidic to Tron bass tones. I only use the pitch tracking VCO on glitching out drums lately (see the end of the video on my sig).
The Future Impact is the most versatile and best at pitch tracking off all I have tried. Best of all, when it glitches on mutes and ghost notes it sound appropriate and musical. This may not be a big deal to many but to me it means I can be myself around the bass neck with out piercing eardrums with nasty high pitched glitches. I would dig some sexier reverb, chorus and delay effects and the ability to use them and eq at the same time, but the effects on this thing are just a small bonus. Besides delay based FX, my only other criticism is envelope control. I wish we could have more control over the curves of the envelope and envelope follower.
Are they worth it:
Markbass Super Synth: ehh
EHX Microsynth: boring after a week
Chunk Systems Octavius: Yes, but more as a Fuzz-Filter-Envelope Follower with presets
Future Impact: Yes, absolutely!
Note: FI is still being developed, it should continue to get better and better. If they could get some better US import support to drive prices down I think this thing would fly off shelves under $400.