Okay, with no immediate replies, I have run IP ROUTE on each of my devices; output is below:

root@GL-AR750:~# ip route
default via 10.0.0.1 dev br-lan proto static
default via 10.0.0.1 dev wlan-sta proto static src 10.0.0.40 metric 20
10.0.0.0/24 dev br-lan proto kernel scope link src 10.0.0.50
10.0.0.0/24 dev wlan-sta proto static scope link metric 20
root@GL-AR750:~#

root@MT300N:~# ip route
default via 10.0.0.1 dev br-lan proto static
default via 10.0.0.1 dev wlan-sta proto static src 10.0.0.45 metric 20
10.0.0.0/24 dev br-lan proto kernel scope link src 10.0.0.55
10.0.0.0/24 dev wlan-sta proto static scope link metric 20
root@MT300N:~#

From a PC connected to MT300N:

IPv4 Route Table

Active Routes:
-------- Network_______ Destination Netmask ___Gateway Interface _______Metric

         0.0.0.0          0.0.0.0         10.0.0.1        10.0.0.11     20
         10.0.0.0    255.255.255.0         On-link         10.0.0.11    276
        10.0.0.11  255.255.255.255         On-link         10.0.0.11    276
       10.0.0.255  255.255.255.255         On-link         10.0.0.11    276
        127.0.0.0        255.0.0.0         On-link         127.0.0.1    306
        127.0.0.1  255.255.255.255         On-link         127.0.0.1    306
  127.255.255.255  255.255.255.255         On-link         127.0.0.1    306
        224.0.0.0        240.0.0.0         On-link         127.0.0.1    306
        224.0.0.0        240.0.0.0         On-link         10.0.0.11    276
  255.255.255.255  255.255.255.255         On-link         127.0.0.1    306
  255.255.255.255  255.255.255.255         On-link         10.0.0.11    276

Hope that’s readable.