Do you mean, are you nuts for thinking that going stereo (given that the particular rotary sim-device has stereo outputs) would yield the best faux-roto eperience? No, not at all! When such effects get to do their thing in stereo, it's startling how dramatically going the bi-way improves that sense of spin!
Korg made a killer roto pedal, the Toneworks G4.
If you could live with a rackmount affair, the Lexicon Vortex does a real nice rotory effect, and it speeds up to or slows down to the selected speed when going from one to another, just like a real live motorized Leslie. And one of the best stereo spacial rotory sims that I've yet heard is the Alesis Midiverb and Quadraverb; they're stunning!
For a high-speed rotory warble, the Electro Harmonix Small Stone phaser actually sounds pretty good!
Or are you really looking for a Univibe stylee? Not so much a fake rotory, but a fake of a fake rotory? That's a whole realm in itself! Whichever Univibe clone or cousin that Teahead's running, sounds pretty Hendrixy-Univibey to me!
Uhmn... does it have to be a pedal, though? If you're going to the trouble of an additional cab or amp anyways, maybe a real live rotory cab of some kind would work for you. A real deal roto (in mono) sounds more stereo than stereo!
I know one guy who uses just the top, the rotory horn enclosure, sitting atop his bf Fender Super Reverb; usually he just lets it do its thing by throwing itself around the room; sometimes, I think he mics it. It always sounds great!
Motion Sound makes a variety of rotory devices, Mesa Boogie also has their Revolver. I know there are others currently out there, but I'm not certain of all of their brand-names.
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Ask yourself- What Would Ren and Stimpy Do?
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