This thing's a beast, I use it mainly with my volca sample to add that analogue oomph that I felt the sample was missing. 
 
It works as a kick obviously but it can also do massive sub-basslines, there are also some good videos of people using it to play melodies via MIDI [see Oscillator Sink]. 
 
Pros: 
Massive sound. 
Same form-factor as the other volcas. 
Fun to mess around on! 
Cons: 
Some blips at the start of pattern-chained sequences. 
Relatively low feature-to-cost ratio (touch FX are cool tho) 
 
Conclusion: 
It's probably my favorite volca, for some reason it's simplicity speaks to me.