I've owned a Fireball II ever since they were released. It's a great pedal that is tweakable for your particular amp and guitar. The construction is amazing and the enclosure is miles above a Hammond box. It's ergonomic, the shape protects the pot and external switch and it looks great all anodized and all. The internal trimmers and switch allow for a good range of treble and mid shaping. It's easy to adjust and sounds great from a mild breakup all the way to really ballsy overdrive. I'm kinda surprised that they aren't more popular really.
I have a Fireball I which was a direct competitor of the Fulltone Fulldrive II at the time. The Banzai was a bit smaller and slightly better sounding to my taste. I've always read great reviews about Banzai products, but their product line has not evolved a lot, that's certainly the reason why they did not become famous.
I had a Fireball II for several years. Didn't dig it that much as a dirt box into a clean amp, but it was a fantastic boost into an overdriven amp. Stupidly, I sold it, and now I'm regretting it, as I've come back around to the idea of boosting my gain channels. Sadly, I doubt I'll find a replacement anytime soon...
Update ~ I found one on the 'bay, bought it, and just got it a couple days ago. Sounds great ... actually sounds better as a dirt pedal into a clean channel than I remembered. Maybe my current amp is a better match for it? But I'm very, very happy I re-bought this pedal.