The USB port is not for sniffing. It is used for powering the Zigbee module.
I use CC Debugger + cc 2530 to sniff the packets. This is rather cumbersome setup. If you want Zigbee sniffer, you should find something else that get your data into wireshark. Once you get your data to wireshark and find the network key, understanding what is going on will be easy.
I do not have keen device. I do not know how to comment about it.
One of the reason I made the dth, I want to have some visibility of what is going on in my reperater. The neighbor info tell me that my repeater is capable to see 13 different devices.
Out of that 13 neighbors, the repeater sees 3 of them as children. The child is a number of end point devices( typically battery powered) that connect to my repeater. These kind of device is extremely optimized so that it only know its parent and communicate any packet through its parent. This should tell me that my router is routing from at least 3 devices to eventually the coordinator (in this case the Smartthings hub).
Zigbee is a complex protocol. I am hoping that the information that I show can give some peek of what is the module is doing without going into sniffing the zigbee packets.