Is the Red Panda unit true stereo or is it a mono effect that combines the L/R inout signal, processes it in mono, and then mixes the processed mono signal in with the passed stereo input? I have learned to be wary, if I care at all for stereo, of guitar pedals that appear to be stereo but that are not true stereo (e.g. Strymon Timeline). Sometimes I care, sometimes I don't.
WMD stuff gets lots of love from the modular crowd, though I don't have any atm. I have several of their modules on my "want" list though, but not their bit crusher. The Biscuit appeals to me personally more as a stand-alone processor for drums due to its interface, especially for drum machines and groove boxes.
...Music can be used to stimulate mass emotion, while mathematics cannot; and musical incapacity is recognized (no doubt rightly) as mildly discreditable, whereas most people are so frightened of the name of mathematics that they are ready, quite unaffectedly, to exaggerate their own mathematical stupidity.
G.H. Hardy in A Mathematician's Apology (London 1941).
They are extremely different really. I'll go with The Geiger Counter first. It has the following features that I'll try and "Pro" and "Con":
+ An ocean of wave shaper algorithms on hand to process both the bitcrushing and downsampling sides of things. They result in sounds ranging from things that would resemble envelope filters (all very input and volume sensitive), to various forms of white/pink noise, to waveshaper distortion, to octaver effects.
- The amount of waveshapes onhand can actually be intimidating, and with no patch memory the results can be nearly impossible to replicate. This is currently being worked on by William Mathewson with a version that you can save patches on, as well as have a wet/dry mix. Unfortunately it's been in production for a loooong time....
+ Input volume is controlled by a distortion preamp that bares much of the sonic qualities of a tube amp.
- This makes it very difficult to get a clean/precise bitcrushing sound. This may seem like it's not that big of a deal, as who uses a bit crusher and doesn't want their sound obliterated? I just state this so that it's clear that this box is a bit grungier and grittier.
+ Wet/dry mix, precise clean preamp, patch memory, a tight but highly usuable table of waveshaper distortions and octaver effects. Everything is highly usable and recallable.
- This in turn also means that in it's clarity and focus it has slightly less possibilities.... sort of....
+ The OTO has a really interesting lo-fi Delay that I've used to some great effect. No negatives there
+ You can download a free low-fi Monosynth (Der OTO) and install it. It's amazing that they just basically threw in an entirely different product into the preexisting architecture. These guys I expect will continue this level of innovation and passion.
+ MIDI i/o
+ Analog multimode filter capable of beautifully sculpting anything you throw it. It can also be used as a Murf-like step filter, a very nice touch.
+ Interesting approach to bit reduction, as the OTO uses a system that either mutes or inverts each of the 8 bits. I prefer this sound to every single non-software based bitcrusher I've encountered.
So if I had to choose it would be the OTO hands down. I could not have that device out of my effect rotation. That being said I do really love my Geiger Counter. Oddly I really like using it on my wife's vocals. It just gives a really characterful overdrive when you want it. One that's slighly muffled, but gritty as hell. If you have the money get both, but if you truly can only get one I believe I've provided some starting point for your decision.