If you have Fritzbox 5490, you do not need this bundle. Fritzbox 5490 already has a "fibre" port. This bundle is needed to use a normal router without a fibre connection.
You can also have this media converter next to the fibre outlet and connect it via Ethernet to your Fritzbox (or another router). This way you can place the Fritzbox in a different location, for example, to get better Wi-Fi coverage.
(I use this bundle and connect the media converter to my Netgear R7000 router).