What is the difference between a 'built in receiver' and a 'mini built in receiver'?

Built-in receiver

The 'normal' built in receiver will plugged in behind a lamp directly on the energy pocket. Those typ of receivers are a bit bigger and useable for ceiling sockets. If you would like to use also a fysiek switch, you need a wireless transmitter (433Mhz).

Built-in mini receiver

A mini built in receiver will be plugged in behind the existing switch that has control over one or more lights. Now you can use also the existing switch, but also the HomeWizard app.