I think I've figured it out. Variax can do it 6 times at once because it's not a real, complex signal with character that must be maintained. That hex (polyphonic) signal is mostly about base frequency, amplitude and some overtones. All the character is added later, so the maths to lower the frequency and the re-stitching of the waveforms to fit the timeframe is not as difficult as in the real audio world.
That said, I do have a Vox pedal which does it a little better than Firehawk, at least for the song I'm playing at it but with a little more latency.
You are quite right that we don't know - and it doesn't matter - how long it takes the ipad etc to get to work. Though it does do it in real time, it could well take too many mS to get going.
I would still take some latency for a "Chord Bender" (you could call it polyphonic, though we know it isn't) if the guys could be persuaded.
Thanks for the voyage of discovery, though I'm still suspicious that the 'warbling' sounds like attempted tracking. Maybe it's failed attempts at re-stitching the wave.