> Is there an advantage to using your own ONT
Some customers might want a dedicated ONT, some might want an SFP+ module, some might want one integrated into their router.
Some ISPs only allow registering one ONT per account and don't allow changing ONT serial. With your own ONT you can have a hot spare available if one fails.
Some ISPs restrict access to ONT information, with your own ONT you can log connection quality data into grafana and setup alerts.
The ONT is directly accessible from the ISP's network, some ISPs haven't provided updates for their ONTs since 2016. With your own ONT, you can ensure you're always patched and secure.