Asus BD4 Outdoor - very disappointed

So I have an ASUS BD4 Outdoor to extend my AIMesh that contains two XD6S units, which work fine.

Out of the box, the BD4 has an extremely weak WiFi signal. To set it up, it need to sit like 15 cm away from it so my MacBook can pick up the ASUS_... SSID it broadcasts.

Integration into my AIMesh works if I connect Ethernet. The BD4 shows up, connectivity is "Great" (green), but it never gets any clients assigned. If I force a client onto the BD4, I get a warning: Due to the current weak connectivity, the client may lose internet access. Rightly so, if I confirm the forcing, the client is offline.

Integration into my AIMesh without Ethernet is a huge hassle. The BD4 has to sit very close to the XD6S for it to pick up unit, and every so often the integration fails mid-run.

I suspect the BD4 unit is faulty. How to I prove that? Is there another likely cause?