This thread is intended to showcase the different ways in which the Shelly devices can be used. This might help a user understand how a Shelly device might be useful to them.
I will start this off by showing how I used the Shelly Bulb Duo (https://shop.shelly.cloud/shelly-duo-wifi-smart-home-automation#322). I have an Insteon SwitchLink Dimmer switch that controls an outlet in my bedroom. After a room rearrangement, the outlet controlled by the dimmer switch was unused and I had no way to control my lamp.
With the Shelly Bulb Duo (~$10 USD), I was able to gain the ability to control white temperature AND I was able to link the Dimmer switch to control the bulb.
Using a trigger that triggers on any Insteon command coming from the switch, I was able to set the action to match the OnOff state of the bulb to the OnOff state of the switch. This allows for the switch to already be off, manually control the Duo and turn it on (switch is still off) and then I can turn the switch off which will cause the trigger to match the Bulb's On/Off to the switch's OnOff - which is still off. I chose this over triggering on a state change because if the switch is off, turning to off again will not change the state and "sync" the Bulb to the switch.
I imaging something similar could be done for cases where you have a switch already in place, but a light you wish to control is not on the same circuit. Depending on the lifespan of these Bulbs, it can be cheaper than having to buy a $50 USD Insteon OnOff module or Dimmer module. Plus you get control of the white temperature.
In summary: Insteon wall switch is able to control my Shelly Duo which is on a different circuit. I can once again turn my lights off AFTER I have gotten in bed!