Know what you're getting into

I think at least one other reviewer may have been expecting a device that tracks like a high-end bass MIDI controller. That's not what this is.
This box can make your bass sound like (or sound like its being accompanied by) an alien, a spaceship (taking off or landing w/ use of expression pedal), a robot monk, a fuzz-wah/envelope (optional expression pedal is nice) lo-fi face melting machine, a synth-wah punch of wet, tight, robot sex... BUT TRY BEFORE YOU BUY!!
Make sure this pedal suits your needs or fits somewhere into your sound or what you're trying to sound like.
It will not track your Jaco riffs; that's probably asking too much of your audience anyway. It will not provide fluffy pad synth to fill out your Creed covers.
Also, for cleaner tracking (on the actual SYNTH settings 1-8) it likes clean input of single notes (NO CHORDS) without a lot of harmonics, so don't put any effects (ooo! except maybe the fx only output of a clean delay!) between it and your instrument. Dial out that growly bridge-panned jazz tone, solo your neck pickup, or pull out the P-bass.
And DON'T PLAY WEEDELY SOLOS AND RIFFS THROUGH IT! It can't keep up with them and it's not meant to.
Do a youtube search on this thing for some examples of what actual talented and creative players and hacks (the good kind) have been able to do with it. Hell, one dude even looped the dry output back to the input for a feedback loop and tweeked on the freq/res and rate knobs, playing the fool thing without an instrument (per se) plugged into it!

A keyboard for your bass

a really great pedal, can produce crazy synth space wahs to the more funky waves. definitely a must for those bassist looking to experiment, or just love the synthesizer but don't want to let go of their bass to play one.

Be subtle and mindful with this effect

Of the 11 synths the SYB-5 has, I'd say only 3 or 4 are use-able. Some of the synth sounds don't sound too great and the Boss techs have a lot of work to do in their bass-FX department.

The secret is to be subtle with it and keep your dry signal up all the way and the synth low. If you want full on synth, you might aw well put the bass down and become a guitar player or play keys.

On some of the synth modes, you can hold the pedal down to increase the intensity of the effect while you're playing.

What I've always loved about Boss pedals is they are 1) true-bypass (I picked this pedal over the Electro-Harmonix synth for that reason), 2)sturdy & break-proof and 3) you can daisy-chain them from the stage-tuner and power a bunch of Boss pedals with 1 power supply.

For now, the SYB-5 will have to do and maybe Boss will come out with a new improved pedal soon.

Unusable.

If only there was a "negative 5 stars" rating available...Latency and tracking issues abound, and the sounds, when you can coax them out by playing veeerrrry sloooooowwwwly are lame - even at the suggested settings for different types of sounds. Sorry, but if I can't get a useable sound out of a stomp box after repeated manual readings and 2 hours of knob twiddling, it's "bye bye stomp box", Thankfully, Sweetwater has stellar customer service, and I was able to return this completely hassle free.