Hey Craig,
I don’t know the internal circuit of the IoT Relay. If it has an optocoupler or a SSR relay (that usually contains an optocoupler), then the green trigger input is galvanically isolated from the switched circuits. It would be worth finding this out.
But generally, I recommend using optocouplers on the outputs of the 25-pin I/O port of Onefinity/Buildbotics controllers, as they use none! And with those, it is even more easy to implement multiple relays on one output.
Many of the pins of 25-pin I/O port of the Onefinity controller are directly the in-/outputs of the AVR microcontroller inside, and usually it is better to protect this microcontroller with galvanically isolated couplers.
And additionally, if you have an optocoupler on every pin, you can make a circuit that can drive more than a few symbolic microampères. The latter is the reason why people use the FOTEK SSR or the IoT relay, and not a real electromagnetic realy, because the low input current requirement of SSRs makes it possible to connect them directly to the 25-pin I/O port pins, but it is generally not recommended. They saved on many things with this controller.
The Masso has an optocoupler on every port:
I plan to build a better breakout board box for the Onefinity controller, with a longer 25-pin cable, and optocouplers in it, and circular sensor connectors for retrofitting inductive proximity limit switches (to get rid of having to use stall homing). I already have most parts here, including a nice case. Don’t ask me when it will be ready, I’m working on it but have many, many other things to do at the same time.
PS: You could ask the sellers of the IoT relay (FAQ) directly. Ask them: “How is the green trigger input of the IoT relay galvanically isolated from the switched circuits (optocoupler/SSR etc.) and can I wire the green trigger inputs of two IoT relays in parallel, in order to be able to switch them both from one source at the same time, but with their switched side on different supply circuits?”