A Tube Zipper is basically a tube-powered pre-amp. Id go with a Flanger Hoax, or if u got the money, a POG. See Blue orchid by the White Stripes for what it can do.
Both make lots of crazy sweet noises, but are totally different. The Tube Zipper is an overdrive and Auto Wah, while the flanger hoax is indeed a flanger, but can do all kinds of crazy noises, not all of which are good sounding like the tube zipper. Both are win.
If you mean the synthesizer pog, I can't afford that. I'm not really looking for stuff like that though...more like blatant psychedelic things