You will need the ONU because the device is used to convert optical signals to eletrical signals. Else you will need an SFP GPON (basically a small form factor ONU) that can be put directly in an SFP cage.

Also you will need a router to dial PPPoE, however the router here is optional. You can dial directly from the ONU/SFP GPON if it has a dialing function or you can dial directly from your PC, however only you yourself can use the internet.