I use a mic made for horns (clip on like you'd see on a sax). It works really well on my stand-up.
this amp is made to give a realistic reproduction of an acoustic bass, but has an EQ, Bass roll-off, limiter, effects loop, and reverb to give more control over the sound...also has two channels and a tweeter, so could plug a guitar into it as well if wanted.
On smaller gigs it would be used for volume... in a larger venue it doubles as a signal processor/pre-amp and a stage monitor. Many monitor systems in the bigger shows don't work well running the Bass through them, and the amp gives the band more control of how much bass they want to hear without it sucking all the power from the vocal monitors.
It also cuts down on feedback. The large surface of the Bass reflects a lot of the floor monitors back into the vocal mics. the amp, behind the Band, fixes this.