I tested it the other day and it’s... awesome!
In a few more words, I felt the clean channel is incredibly responsive and stable, the Gain stage is very accessible and great in almost every position of the volume knob. You set everything to 12 o’clock and only have to tweak here and there. Pretty much an instant great sound. And overall, it’s not very loud for a 100W-amp.
They had a Sonzera 50 head as well and it was clearly moving more air, especially the Gain channel.
If I had the money right now, I would go for the J-MOD, but the clean channel of the Sonzera is similarly great - for about 1/10 of the price. The only thing I would have to get used to is the Gain channel on the Sonzera.