wanted to but I need (have) to wall-mount it so AX55 or AX58U is the only 2 options. But AX58U is twice the price of AX55 here and seems to only offer supported-merlin-firmware but nothing else :| so maybe I'll just pick the AX55 and be done with it.As long as the two routers are using AiMesh v2.0 (and assuming they both have the latest firmware available, they should), then it should work.
If you have any specific problems, you can ask for help here on the forums.
Given the above, I would not recommend that model you're considering (although it may be sufficient for use as a mere wired AiMesh node). The RT-AX68U is highly preferred to use with your RT-AX86U main router (and they will use the same firmware level too).
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