Hi there,
I just received my batch of white series switches and preparing everything to install them.
Something that is not explicit in the manual or page is if they will extend the mesh network or act as a repeater for other white switches far from the hub or for any other thread device. My zbdongle-e (enabled for thread) will be in the basement and the plan is to install the switches all around the house (exactly like my current z-wave network with 20+ red series installed (working flawlessly)), but I’m sure some will be far enough to talk to the dongle directly.
Yes, I know I should had research about it before, but too late for that. Got exited last year reading about matter/thread and assumed the white series will be similar as red ones, since they are main powered.
Can somebody confirm?
I’m not sure anyone has tested this explicitly, but similar to Zigbee (and Z-Wave, but Thread draws particular inspiration from Zigbee), mains-powered Thread devices are supposed to be “routers” (i.e., mesh network extenders or “repeaters”) for your Thread network. Thread is actually a bit smarter about this than Z-Wave and with multiple Thread Border Routers (TBR) can even meld together distinct Thread networks over your LAN that are not able to reach each other wirelessly. While this is probably not ideal, if you have multiple TBRs, it does mean that if this describes your setup (e.g., multiple Apple TVs or HomePods or Nest Hubs or whatever), complete wireless coverage with Thread alone may not be necessary like it is for Zigbee.
One source: https://www.threadgroup.org/BUILT-FOR-IOT/Smart-Home
Of course, it’s possible (but unlikely) that something is unusual about these devices…
They are Router Eligible End Devices (REED) and are capable of acting as routers. If you have more than 23 thread routers some may be demoted to child devices.
Update: Bad news. Mesh is not working.
I have 6 installed so far, an the last two on the far side from the controlller don’t get connected. Even though they are a few feet away from the last switch connected.
A bit disappointed, but this is a reminder for me to first get answers before purchasing 
Thinking on replace them with Zigbee.
Anyone interested on 10 thread switches? 
What you looking to get out of them?
I have one switch that refuses to be added to my Apple Home ecosystem. It is about 25 feet from another switch, and I just relocated my SmartThings Hub closer with the hope it would extend my Thread Mesh network. Still a no go. Any suggestions?
Fixed. Had to pair switch with SmartThings first. Ended up resetting both switches and pairing to relocated SmartThings hub. Pairing to Apple Home just didn’t work given the distance from location.