> voltage is relatively easy, the frequency - if it uses line frequency for timing - less so
Actually, the voltage doesn't matter, the module's HLK-PM01 is an all-voltage power supply. The only electrical issue would be the kit's 1mm² (AWG17) leads for the external relay. Sufficient for Europe, where 1200W means 5.2A, but 110V machines usually require thicker leads, e.g. AWG14.
On the firmware side, 60hz instead of 50hz probably is a deal breaker for the phase-fired controller in the firmware and thus pressure profiling. It would have to take the different voltage timings into account. While some attempts have been made to that end (waveform is sampled), there was no way for the developers to test it. It's quite likely that it might not work at all or work badly. Therefore, using it with 60hz is not recommended. Sorry.
> Would this work on a Spaziale Mini Vivaldi II?
I've seen it installed in a Vivaldi, but only for pressure profiling (next to the original controller, which still did temperature control and the rest). The solution for the display was a 3D-printed bezel
The pump output of the original controller was connected to the SNS input of ito. For the firmware, mains voltage at SNS is a signal to start the pump at ito's relay #1. Thus ito was threaded into the controller-to-pump connection to add pressure profiling.
The solenoid valve remained connected to the original controller (downside: no dosing with the added module). The pressure sensor was installed at the grouphead
, where suitable threads are available. That's a position after the solenoid, so it reads 0bar if the machine is not in use - instead of boiler pressure. Useful in this case because it means that pressure profiling can be set to kick in at 0.7bar. Thus, any use of the pump by the original controller to refill the steam boiler is not subjected to pressure profiling (solenoid off -> 0bar at sensor -> no pressure profiling).