I think it will be fine if u toggle the reset setting to erase user data. As far as I know, system data and user data are stored in different partitions. And if u reset ur phone through that reset option provided in system settings, it will wipe off all data in user partition. Since smart phones use SSD rather than HDD for storage hardware if it is reset, it's gone for good, permanently.
btw if u still worry that somehow ur data is stored in system partition, u can reset the system partition by simply toggling on unlock boatloader option. Ur phone will restart and reset both the system partition and user partition.