The chorus in the Blue Valvetronix amps is modelled after the legendary Boss CE1 chorus. The CE1 uses the chorus circuit from the Roland JC120 jazz chorus solid-state amp.
The Boss CE1 actually had two effects - chorus and vibrato. It could be used either in stereo or mono, and it had a switch for high or low impedance. As you'd expect, only the chorus effect is modelled in the Blue Valvetronix.
With modern chorus pedals, the depth and speed settings are separate and modern units are designed such that you can max out speed and depth and still stay (reasonably) musical albeit 'metalic' sounding at extreme settings.
In the CE1 there is only a single control called 'intensity'. This cleverly interacts both speed and depth at a specific combination 'algorithm' such that the chorus remains musical pretty much wherever you set the control. At its highest setting it's just on the brink prior to 'warbling' and crossing over to a 'non-musical' tone.
The CE1 was the very first chorus pedal and its unique design meant that you cannot use the depth and speed controls in your Valvetronix as you might do on a modern day chorus pedal - you have to balance them together interactively to replicate the single intensity knob on the CE1.
If you set the V'x chorus speed up to 9:30 O'Clock it will sound musical with any depth setting. If you set the speed higher you will have to wind back the depth proportionately to replicate what the 'intensity' knob on the CE1 does. Otherwise you will hear a dreadful and unmusical warbling! This is not a fault of the V'x amp, but is precisely because the CE1 is modelled surprisingly accurately.
It's this lack of understanding that has given rise to some V'x users saying they don't like the V'x chorus because the chorus sound they are comparing it with are more modern digital chorus units that can provide very deep choruses (some with a 'metalic' quality) at pretty much any depth or speed setting, and because when they try and max out the effect they get a horrible non-musical warbling.
The CE1 was a much, much more subtle effect albeit more limited by comparison to more modern chorus pedals. If you watch you-tube demo videos of the CE1, you can better understand the CE1 and appreciate more how well Vox modelled its chorus effect and how subtle changes to the intensity knob (depth and speed on the V'x) could create a different ambiance and feel.
Here's a good video to watch: https://www.youtube.com/watch?v=AFtg06TXUA4