Question about ASUS ZenWiFi XT8 WiFi 6 AX6600 (2 Pack)

The product should be v2, I got it a few years ago and it is HW v2.
You can connect a device via network to the main router and create a wlan mesh network.
I'm fine with this, I don't know the BD4 model, a quick comparison with chatgpt shows that:
XT8 is superior in everything: faster, more stable thanks to the dedicated backhaul, better for large or multi-storey houses.
BD4 is a simplified and cheaper version, good for less demanding environments.

I bought the XT8 a few years ago. As the update frequency is slowly falling asleep, I recommend buying a successor product. I can't say whether the alternative OpenWRT runs on it.
Regarding 2: This is my configuration: Both run as access points, 1 device has a LAN cable to the local network and the second then goes into the mesh via WLAN.
I have never had any performance issues. More like mesh connection problems. In my opinion, the out-of-the-box configuration does not work 100%.