Best in class, hands down
I just bought one of these. The quality of the amps and the "organic-ness" of the modeled tube gain stages--compression, crunch, harmonic richness--are very nicely done. Zoom's tech literature says they created a custom chip for that, and I have to say I'm genuinely impressed.
I tend to build patches from the ground up, even if the stock patches are good. I start with an amp model. I generally prefer combo models instead of head+cab models. My first custom patch on the MS-100BT started with the "FD Combo" model, which they say models a Fender Twin. I put a "Comp" in front, and a "Tape Echo" after. Then I tried several distortion pedal models in front of the "Comp". For a while settled on "Dist 1". I figured I'd turn on/off the distortion as needed on that patch. Then, I put a "NoiseGate" after the amp before the echo. Really good patch, so I saved it as Crunch LZ. I loved the clean tone w/Dist 1 off, so I saved the identical patch to a new location as Clean LZ. Then I became curious what it would sound like with pure amp/tube crunch instead of using a Dist 1 in front of a clean FD Combo. So, I removed Dist 1, and turned the Gain and Tube knobs to 100%. Very sweet! Surprisingly sweet. So I saved that to a new location as Trunch LZ (for "tube crunch"). I set Clean LZ as patch A in the chain and Trunch LZ as patch B, which means when I step on the switch while in list mode, it cycles round-robin through A, B, A, B, etc. (If I set another patch as C, it would cycle A, B, C, A, etc., when I stepped on the switch. I just needed the the two patches, though.) This is the setup I used live. Just the MS-100BT and no other effects/modeling gear on stage. I got four separate compliments about my tone from musicians, and girlfriend said "sounded great". The last time I got a flurry of tone compliments like that was the first time I used my AxeFx2 live. (I LOVE my AxeFx2, by the way.)
One drawback of the MS-100BT is its size and limited physical controllability. I can either turn a specific pedal model on/off within a given patch (at least with my feet), OR I can set patches a A, B, C, D, etc., and cycle through them. The last option is the most practical for me, though it is still fairly limiting compared to the crazy flexibility of (for example) the HD500X or (especially!) the AxeFx2. However, this constraint forces me personally to make the most of the patches, how order them in list mode, guitar volumeetc. Since this pedal is Bluetooth--and, by the way, the iOS software is really nice (I'm a software engineer; it's well done)--I'm wondering whether Zoom might introduce an outboard Bluetooth controller for this gadget.
Bottom line: major home run for Zoom. I am thoroughly impressed with the sonic qualities of this all-in-one pedal, and I'm impressed that they jammed all of it into a diminutive little stompbox. The sound is gorgeous to my ears, and I'm impressed by the iOS app that lets me preview patches. If this could be operated via an outboard Bluetooth controller, it would be perfect. Still, I am thoroughly impressed with it as-is.