Ampeg Scrambler Bass Overdrive

If you like the sound of an overdriven SVT tube amp, this is the pedal that you'd want.
The tone is very thick and gnarly when it's running hot. If you try to play with low drive/master volume and high treble, it completely drops out the low end of your tone. Because of this, it is often better to just crank the drive on it and use it as a fuzz box. This way, you'll get a gnarly fuzzy tone, and still keep your bottom end.

On the other hand, if you're looking for something that will just put some grit in your basslines, settle for a Boss pedal or a SansAmp unit instead; they will serve your purpose better.

Long story short, if you're a sucker for overdriven SVT sounds and like to have fuzzy, thick bass sound, it's absolutely worth your money.