From one of the reviews:
Very carefully!
It is not galvanically isolated. The potentiometer wires are also galvanically connected to the mains. You have to solve the touch protection! Install a FI relay! There is nothing to limit the switch-on current. Appropriate NTC installation is recommended! No noise protection. It is necessary to install an appropriate suction guard! It can be used after replacing the deficiencies.
With the potentiometer at mains potential, it is not just a matter of throwing in a DAC.
Note that another version of the controller exists with a 0-10V input for speed control:
