Forgive me for jumping in on the end of an interesting discussion (and for being a bit of a beginner)
I was planning to install a Zappi-2 (when/if it becomes available) but after many promises of an end user API over the last year my hopes were finally dashed with an email from one of their directors confirming they will not be developing one so I have cancelled my deposit.
Looking for alternatives I came across your EVSE which ticks all boxes but this thread concerns me.
I have a TN-CS site. While £550 is a saving over the Zappi, adding a £300 type B RCD is a bit of a sting in the tail. Is this just something I have to accept or is there any other option?
Apart from the RCD issue, is there a reason why your EVSE steps up and down in 1A steps? The Zappi seems to follow the export CT to within about 50W. Here I am going to expose my ignorance about the PWM signalling but is this something that can be improved in future?