L&LD
Part of the Furniture
The RT-AC66U (original, 'classic') and the RT-AC66U_B1 are not the same router. The '_B1 version is based on the RT-AC68U but with better hardware than the original of that model (has been updated and marketed with many different names in various markets).
The RT-AC66U is not recommended. But the RT-AC66U_B1 is.
The RT-AC66U is not recommended. But the RT-AC66U_B1 is.