Hello  @ChinookBG 

Thank you for being interested in TP-Link One Mesh range extenders. 

Dual-band range extender will broadcast both 2.4Ghz and 5Ghz Wi-Fi bands for the network client devices, regardless OneMesh is ON or OFF.  This means your laptops or phones can use two bands at the same time when OneMesh is enabled on the range extender. 

I think the reviewer may want to talk about the 'half-duplex mode' on the range extender, the extender talks to the main router or the wireless client device in either way, not at the same time, that will in some extent affect the speed of the extender (compared to the Ethernet connection). But this does not affect the Range extender operating on both Wi-Fi bands and can provide internet for network devices through both Wi-Fi bands at the same time. 

Hope this help answer your question.