Ok I just got this like a half hour ago, so I thought I'd post my initial impressions and some soundclips.
What is the Rotovibe?
It is NOT a Uni-Vibe. It has a lot of similarities to the Uni-Vibe, but I can tell you straight away if you're looking for the Uni-Vibe tone, this pedal sucks. I've owned several Uni-Vibe pedals, and this is slightly different. The Rotovibe is meant as a leslie sim, like a Uni-Vibe, but like the Uni-Vibe I don't feel it does a particularly good job of it. It does have it's own cool sounds though.
How does it work?
Switches on and off like a wah, treadle controls speed, switch on the side to switch modes, knob on the side to control intensity.
Does it keep the bottom?
So far with my Jazz Bass it's fine in the chorus mode, sounds a little weaker in the vibrato mode. But note that there are internal trim pots, one of which supposedly controls the amplitude modulation, which is part of the effect. I just turned it all the way down. Amplitude modulation is cool for bass when you want to physically feel the effect (through the modulated bottom end) and it can make you seasick, but I'm trying to be a little more practical and depending on where you've got your rate set it's a gamble if your bottom is going to be there on the attack on 1 when you're modulating amplitude. I'll let you know more about how practical this thing is on bass when I use it more, but I have been able to get mileage out of Uni-Vibe effects in the past which are somewhat similar to this.
What does it sound like?
There are two modes, just like on a Uni-Vibe, Chorus and Vibrato. The chorus, also like a Uni-Vibe, is a phasery kind of chorus. The vibrato is a pitch modulator. Most people find the chorus much more useful. Ok that's enough talking, I'll just let you hear the effect:
First I have a Vibrato setting add some color to a riff:
http://media.putfile.com/Roto1
And a slow chorus adding color to a different riff:
http://media.putfile.com/Roto-2
A phasery tone with a low bassline:
http://media.putfile.com/Roto3
Some jazzy style fast chorus:
http://media.putfile.com/Roto4
And though I don't feel this pedal does a good job of it, I had to try Led Zeppelin's Heartbreaker:
http://media.putfile.com/Roto5
Maybe I ought to up the intensity on that one? Anyway, I kind of liked some of the Uni-Vibes I've used better than this, but with an amplitude modulation fix this is a little more practical on bass I think. But I'm not sure how I feel about these tones, so PLEASE if you have an opinion, good or bad I don't care, do share it.