Hi everyone, I have a question regarding second router.

I've moved to a new home and relocated my unifi. The house is 2 storey and the wifi coverage upstairs is bad. My phone is disconnected from wifi (2.4hz) most of the time.

My budget is cheapest as possible since i only need the internet for social media browsing. I am thinking to buy a secondhand router (Fiberhome AX1800, similar like current router) for upstairs since the connection point is provided by the developer.

Is this method valid? since i saw some postings on Carousell saying that the fiberhome cannot be as second router.

is Xiaomi and Fiberhome router compatible? i thought can only use same brand as range extenders