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.
Ken