I have a wifi scale (Weight Gurus model 0396, 2.4 GHz only) that worked fine for years with my AC66U_B1 when it was my primary router.
I just switched to using a new AC86U as the primary router, same SSIDs/passwords/etc, running Merlin 384.19 and AiMesh, and now use the AC66U_B1 as an AiMesh...