@ hajar’s device handler and associated apps are the best there is. They really exploit the features built into the dimmer 2.
The reason for needing the bypass, is that the Dimmer 2 needs power to run. To power something you need a live and neutral. Unless you have a neutral wire, you need to use the neutral in the circuit, which effectively runs through the lights (this is usually called the ‘switched live’ as it needs the live switched to it in order to complete the circuit).
The Dimmer 2 can never be truly off, as it needs power to accept commands. It needs/consumes a very small amount of power, and is effectively at ‘minimum brightness’ rather than off. This minimum is enough to make some low power bulbs blink or stay on.
The bypass is just a resistor which absorbs this extra power, and doesn’t pass it on to the bulbs.
If it were unsafe, it wouldn’t be for sale. The amount of power going through the bypass is tiny when the lights are off. It really just goes to show how mega-efficient LED bulbs are.