They're saying 8ms real-world latency on the proprietary 2.4GHz protocol with up to 4 devices per hub. Worse when using Bluetooth compatibility.
I get very annoyed by the atrocious audio delay of Bluetooth, so I'll keep my long USB cable ready.
P.S. I am aware of USB also not being zero latency, but it is the lower bound, the dongle is USB as well.
Raw 802.11 with no IP stack can get below 5ms IIRC