How to set up a repeater with one Wi-Fi network?

Question

WiFi

Explain who is on the fingers.
What I want:
There is a Zyxel Omni II with a 4G modem, but its wafer is not enough for the entire site. I wanted to use TPLINK 3420 as a repeater, like one wi-fi network, and I walk around the site and the device takes the most powerful signal and everything is top.
What I got:
I flashed RusBie4G firmware. I set up a repeater, the Internet takes from the zuxel, but distributes it to another Wi-Fi network. It turns out that you need to manually reconnect when moving around the site. On OpenWRT, I didn’t get something like that.
What am I doing wrong? Or what I want is not from this area at all.
By the way, I read about the drop in speed when connecting two routers to each other via a wafer. And if they are connected over a twisted pair cable, but the speed will be the same as on the master?