Your Flint has a newer CPU that’s ~ 67% faster than the Velica & features a NPU (Networking Processing Unit). One should be your main router.
“Using Repeater means connecting the router to another existing wireless network, e.g. when you are using free Wi-Fi in a hotel or cafe. It works in WISP (Wireless Internet Service Provider) mode by default, which means that the router will create its own subnet and act as a firewall to protect you from the public network.”
“Extender. Extend the Wi-Fi coverage of an existing wireless network.”
If you’re looking to keep all the connected Wi-Fi clients on the same internal network/LAN subnet you want Extender.