So my Mod Duo X came...
I almost sent it right back. So incredibly noisy. Put a ground lift on and solved the issue, but...

Come on, ModDevices.

I had to dig that solution up on my own, because I sent a message to ModDevices and never heard back, but at least there’s a forum which is helpful.
Here’s my initial take on it.
Seems solidly built. Definitely good for my desktop needs. Buttons and knobs all feel fine, though I think the paint that covers the button/lights may wear over time. It comes with a carrying case that I shall promptly put in my garage and never look at again. No full manual, which is a shame. Not everything is clear and the only manual seems to be an html page, so if you think you can even print a pdf and read it at your leisure, you’re SOOL.
Some things are disappointing. I’d read it was Bluetooth...but it’s not, unless you buy a USB Bluetooth dongle. Only $15, but when you drop $800 on something, maybe it should have the Bluetooth built in.
I went though most of the effects. They’re all good, but mostly vanilla. I think the idea is that you can squeeze character out of them with the way that you can really hook anything to anything, even audio loops. So, you’ll have a very basic sounding digital delay but you can put it after a wah pedal and touch it off with a bit reducer. The standout character effects were actually the distortion effects and guitar amps. No noticeable aliasing and they sound good. They sounded really excellent on the Prophet 12. I had this noisy keys patch I made and a bit o’ distortion, tremolo and some ping-pong delay was all that was necessary to feel like Thom Yorke on a gray fall day. Would they hold up as a stand alone guitar amp modeler and effects box like a Heix? Maybe.
What’s really missing is a good tape delay emulation, and stuff like that. There’s a good Leslie, but what about a Bi-Phase? Nice Tri-Chorus, but no CS-TERC emulation. Decent reverbs, but no spring emulation. So, if you’re looking for analog style delay and modulation effects, there are some for sale (more on that later) in the software marketplace, but it doesn’t seem to come with many. Oh, no multi-tap sequence style delay either. Definitely some gaps. What I hope they do is write a delay that has a way of putting insert effects inside the feedback loop. That alone would really open things up. In a sense, having effects with a lot of character isn’t that much of a need with something like the Prophet 12, which has buckets of it’s own character.
So, a quick trip to the effect store and there is indeed a tape delay emulation. So that’s sort of a double edged sword. Yeah, the ability of your Mod Duo will continue expanding beyond what it came with, but you have to pay for a lot of the additional algorithms, unless you can code your own, which they encourage. How much is that tape delay? I have no idea. It doesn’t seem to have a price listed at all... maybe free? Maybe you have to buy it from inside the editor interface? I’ll have to dig around. Might be nice if there was a printed manual.

A lot around the edges does seem like a work in progress.
The real magic of it is that you can really just go sick with effects and routing. I’ve not yet tried anything too complex yet, but if you go though the on-line patches you can easily see the power of what can be done. It’s also
very easy to patch things up. There’s lots of ways to use crossovers to segregate frequency ranges and mixers to blend things back in. The power is huge. The interface graphics are a mixed bag, and frankly I wish they just looked more like how NI does their new effects. Clean. 99% of the time I’m opening up the full deep dive interface because often the UI designers hide a lot of good parameters. That interface is clean and easy to use. The look of a lot of the effects look like bad Synthedit effects from 2005 and on my monitor they’re often hard to see even when zoomed in, so I’m always just opening up the full interface.
The other great thing is that you can freely assign any parameter to one of it’s knobs or buttons, which is sort of the major point of it for me.
So, overall, positive. I think if you’re a synth player who wants something small to set on top of a synth to mess with in some sort of ambient setup, this would be a great box, no doubt. Especially if you’re willing to put in the time to create custom patches, which is easy and pretty fun. I think you can get better effects from Eventide, Strymon or Empress, but not nearly as flexible or as creative. Could you put together something as interesting in a modular software system like MXXX or Guitar Rig? Maybe. I must admit, as I was putting together little “pedalboards” as they call them, I could not help but think, “well, if I was doing this in Guitar Rig hosted in Maschine...” Tomorrow I’ll to a hard side-by-side to see if it really makes sense.