Question about TP-Link Re450

I wouldn't use repeaters because they are a mess and also reduce the speed. It would be much better to buy a WiFi mesh system. This gives you WLAN coverage in the entire area, where the individual WLAN devices always connect to the stronger transmitting WiFi mesh router. With repeaters, there are interruptions when you leave the transmission range of one device and the devices hang on the connected repeater until the connection is broken. Nowadays, that's a mess.

My recommendation:

TP-Link Deco M4 AC1200 Dualband WLAN Mesh 2-pack

This is also available as a very reasonably priced version with 3 mesh routers:

TP-Link Deco M4 AC1200 Dualband WLAN Mesh 3-pack

The first mesh router device is connected directly to the existing router, the second device is set up with the mesh system and can then be moved to the other room. The WLAN of the existing router is no longer needed.

According to Google, repeater series connection should be possible.