Re: How does a talkbox work?
Originally, talk boxes took the speaker out from you amp, or a separate amp, and ran it through the tube. Then, you used a vocal mike to pick up the sound and amplify it through the PA. I believe the Rocktron Banshee has its own amp - when you switch it on, it turns off the guitar signal to your amp and amplifies the guitar on its own, through the tube. You still need a vocal mike to amplify that to the audience.
IIRC, the new cheapy Danelectro talkbox goes one further. It has a little condenser mike attached near the top of the tube. The pedal amplifies the sound, and runs it through the tube, then the mike picks up that sound and the mike signal runs back through your guitar amp. No PA needed. Of course it probably works better with a clean guitar amp. I wouldn't want to run that little condenser mike into a full-tilt Mesa Recto, for example.
If you're a guitarist that sings backup (or lead for that matter) then the mike/PA requirement isn't a big deal... your vocal mike is there already. Actually, one of the slickest things I ever saw was Joe Perry's setup (Rocks era). He had his talkbox driver in a sack on his back, and could move around the stage, using any mike available, sharing Tyler's, etc. Sweet Emotion - just too cool.