Hi.
I'm really no expert on Shelly UNI, since I just got my first one today, so I am yet to experiment with it. As for the other Shelly's I have installed plenty.
The way I see it, try to think about the Shelly's (1, 1L, 2.5, 1PM, etc...) as relays. They have a way of switching something on and off. Shelly 1 even has what we call a "dry contact". This means that you can have different input and outputs of voltage.
Shelly Dimmer 2 and Shellhy RGBW2 are also relays, but in both their cases, they offer a certain degree of control, as they allow you to fine tune things as you please.
As for the Shelly UNI, it tends to allow you to operate things. For me it will be used to opperate old devices or appliances. So instead of just powering up or turning off a socket where I connect my coffe machine, I can actually opperate the button I use to either pour an expresso or a long coffee. It means that you control the machine functions and not just its power supply.
Based on what I investigated before buying it, it allows you to even take a step forward than this example, as it brings you the possibility of connecting sensors to it, while you can still operate machines or appliances actions. Sensors + controllers = loads of possibilies if you're looking for automation. Of course they only work with lower tensions, like from 12V-36V, but still it is amazing what a litle device like this can do.
What I am yet to figure out is the way to properly work with them. I'm saying this because all other shelly's come with proper cover, and have well built structures. This one kind of makes me think that will bring about issues when you're trying to hide it or make it fit some small space, as it can be damaged while you're working.
I hope this was any help and if someone finds I said something wrong, please do correct it.