Phoenix is correct about the backhaul. It's the reason I always strongly discourage my clients who say "I'll just get an extender." WiFi extenders might be the least successful consumer electronics devices I've worked with in my career. Almost all of them stop working at some point for one reason or another, and even if they're working at peak performance, historically they only worked by halving the bandwidth for any device that's connected to them. And they're also terrible at handing off devices.

I'm a HUGE Unifi fan, and I've used their products for at least 8 years now. As we speak, I'm doing a major network upgrade, installing some of their latest home switches on my network, including a 16 port POE model that I plan to use to power a whole bunch of stuff, and a couple of their new tiny switches that are powered by POE.

But I have to admit, I haven't had a ton of success with Unifi wireless up-links in the past. There's been times where I got it to work, but the connection was measured in Kbps. Nobody at Ubiquiti could explain it and I never figured it out. Granted, this was very long ago, and they're very very good at iterating their hardware, firmware, and software. I need to give it another shot, because I've heard about setups from the Ubiquiti Reddit group where they're linking 4-6 APs in a chain without trouble, and that's pretty incredible to me.