The green terminal block seems rather fragile to me
No my original built-in were remarkably reasonable.
I have replaced the existing terminal blocks with Phonix plugs/sockets. These are designed for a nominal cross-section of 2.5 mm2 , a nominal current of 12 A and a rated voltage of 320 V (III/2).
They are touch-safe so that I can safely disconnect them during operation without having to switch off the heating system. A pure passive measurement, different from the way I worked with the shelly.
However, only a few mA go through them for operation and volt and frequency measurement. I have exchanged the blocks so that I don't have to disconnect any wiring when I need to access the box.
Instead of taking the voltage from each module of the heating system, I only use it once, as everything is the same phase and comes from the same supply. So in your schematic picture these are exactly the thin blue and red wires.
No power for the pump, fan, solar pump ....
