I've been looking at Z-Wave switches and there are "companions", "controllers", "dimmers", and "relays". "Relays" I assume are electro-mechanical relays. But what are the differences between the other switches? Or is it marketing?
The switches called controllers are able to send out commands to other devices. Similar to Insteon linking. Unless you want one switch to activate something other than the primary load, a controller switch is not needed. You will need a Z-Wave device called a controller.
Dimmers are just that, they are local or RF controlled dimmer switches.
I've never used a companion switch so I can't comment on those.
I have a mixture of Intermatic and HomePro (ACT) wall dimmers, four of each right now. I have read that the ACT switches my not be as good as the Intermatic in the RF world. In my small 1500 sq ft house both types seem to work well.
Just to clarify, there are at least two types of Z-Wave devices that can control other devices: routing slaves and controllers.
Here's the breakdown of device types (roughly--there are more possible):
Slaves: things like lamp modules that are controlled, but don't initiate conversations.
Routing slaves: same as slaves, but can also start conversation with up to 15 devices (5 of which can be routed). These would be things like 3-way switches.
Controllers: devices that can control any other device in the network, have a copy of all the network routes, and are also sometimes controlled. Typical examples are in-wall zone controllers, high-end light switches (that can talk to lots of devices), USB sticks, and portable remotes.