Multi WAN load balancing/failover and devices

Installing and Using OpenWrt
1

I have an unused ZyXEL GS1900-8 switch with openwrt already installed.

I think mine is the same than this with 8 ports instead of 10.

I am brainstorming at the moment.

Should it be possible to use the ZyXEL GS1900-8 with mwan3

Goal should be load balancing and failover between VDSL2 and mobile internet.

VDSL2 would be probably used with a FRITZ!Box 7530 AX or the old version without AX (maybe the old one with openwrt, not installed at the moment)

For mobile Internet I would like to use a MikroTik Chateau LTE7 ax, where openwrt is not possible. I think for LTE or NR openwrt is risky. Am I wrong?

The alternative is to use mwan3 with an Asus TUF AX6000, using openwrt.

2

The GS1900 is a switch, not a router. Therefore while it is capable of routing when OpenWrt is installed, the hardware inside the device is not optimized for such purposes. As such, it will be extremely slow -- in the range of ~20Mbps throughput when routing.

This is a much better choice. A router can route efficiently, so yes, this device would be a good option.