EZ(Easy) mode: 

In some literature, it is also referenced as Smartconfig or Smartlink. It means that the mobile App sends a UDP broadcast packet or a multicast packet containing the SSID/Password into the air. The Wi-Fi module of the device will receive the UDP packet as long as the UDP organization form is recognizable. SSID/Password will be decrypted in the received UDP packet and sent to join the Wi-Fi router.

AP (Access Point) mode: 

The app connects the mobile phone to the smart device by the SSID of the Wi-Fi module. The mobile phone and the Wi-Fi chip directly establish communication, sending the SSID/password to the smart device to join the user’s Wi-Fi.

The EZ mode is easier to use and quicker to set up during the initial setup. 

However, AP mode has to be used in some scenarios that some mobile phones and devices are incompatible with the EZ mode.