Am I going to blow something in one of my cabinets?

Eh, you're not really going to get "super lows".......I think you'll find that octave pedals don't track very well below roughly D on the A string, so you're not going to be putting anything out that's lower than a typical 5 string bass with a low B. Some pedals will track a little lower than others, but still, you're not going to be getting sounds that are an octave below your low E string or anything even close. In other words, you gotta play pretty high notes for the pedal to work well, so you're not going to be getting any uber-low stuff out of it.

Octave pedals are kinda cool because you get a pseudo 8 string effect out of them. They're very handy for filling up sonic space if you're in a 3 piece band.

 

Nah, no worries. The pedal just won't go low enough to cause you any problems - the tracking will start to flake out and it'll sound like crap. Don't get me wrong, they're still very useful - but you'll need to spend a little time playing with it to know it's limitations and what it "likes" best.

Since the Octabass, like most octave pedals, generates a note one octave below the note you're playing, not an octave above, you won't be producing any additional highs, so no danger to your horn either. Even if it did do an octave up, you'd still be WAY below the frequencies that your horn is capable of.