Philip @ Pusherman kindly sent me one of these to test build. It’s a rework of the Bastl Cinnamon multimode filter, with a couple of extra bells and whistles like voltage control of resonance.
Build wise, it’s straightforward common 0603 passives and SOIC ICs, not particularly densely packed, and clearly laid out. There’s a IBOM in the build documentation on Barnaby Walter’s github. He’s also provided all the KiCAD files, so there’s all the info you’d need if you had to troubleshoot anything.
There are three things to calibrate – the V/Oct tracking, the resonance amount, and the drive switch that pushes the usual sine wave from filter self-oscillation into a sawtooth. The calibration instructions are the same as for the Cinnamon, and are detailed here.