I have a number of "C boxes", "R boxes", "L box" and some RC boxes. I find them very useful.
The link shows the smallest capacitor of 0.1pF. I find when the capacitor value is below 50pF the stray capacitance causes errors. I think the capacitance of the input connector is close to 1pF. The PCB capacitance is many times that. There are 32 switches, each having capacitance. How can you get 0.1pF? I don't think this product has been tested. My guess is with all the switches open, (0 pf), there will be 30 pF or more.