Yes, it is a potential renegade device on your network, similar to IoT devices or a computer of unknown origin. Modern SoCs are computationally capable, cheap, and would easily fit inside a commodity consumer switch.
I stick to well known name brands. And in any case, it remains critical to robustly secure all your devices even if they are on your “secure” LAN.
Generally the most you can expect from WiFi is about 500 mbit. Distance, radio interference, radio regulations, and client WiFi limitations lead us there.
Sure, you can get higher speeds in the same room, or with a very capable (rare) WiFi client, or if you live in a rural area without any competitive radios.
But otherwise, don’t set your sights as high as the marketing garbage on the WiFi router’s box, because it is not going to happen.
How big is your place, and how many people live there? That way someone can help you select the right router for the environment.
Can you reach your service from another machine on your internal LAN? Are you confident that your ISP isn’t blocking via rule or NAT? What port number(s) are you trying to use?
I’ve had fine reliability with the Deco X10. Cannot speak to the others.
It is impossible to know if this is Ethernet via the photos. “RJ45” style jacks are used for numerous applications.