Z-Wave Wall Switches and Add-Ons?

Confused a bit by these cheaper ‘Add On’ switches. Can someone explain it like I am a 5 year old? Are they just to be used on the other end of a 3-way, multi-switch application?

That is correct.

You need a main switch and then the add-ons allow you to make 3-way, 4-way, 5-way setups.

The cheaper switches dont switch the power at all, they are remotes for the zwave switches. So if you have a 3-way (like a hall light that has switches for it in multiple locations) you only buy 1 dimmer/switch and the rest will be ‘addon’ remotes. Since they have no zwave tech, they arent expensive.

Could these be used as “virtual” switches that trigger a smart app?