@GRB 

response from support:

To clarify - 

 these data rates are blank in the app - please explain how to enable these

@TP-Link 

customer services say:  'after checking ourdatabase, it is normal for the deco not show the speed of clienct ...  that's the product design, we can't change it ' 

why show these rates in app, if it's not supposed to work ?

The list of devices never shows anything, no matter how long I leave it.

Clicking through to a device it showed 9kpbs download, while the MacBook was at 5MB/s downloading an Ubuntu ISO file.

Checking all other devices, by clicking through shows exactly the same 9Kbps download and 2Kbps upload for every device. Which is clearly wrong.

Edit - update:

All devices now showing 0Kbps now when clicking through per device.

@GRB 

Interestingly, whilst watching the app -  the number of devices suddenly dropped and the globe icon showed a red warning - and for a brief period the devices in list showed a realtime data rate for upload/download.

The device count went back up, the warning on the globe went away, and the device rates went blank again...

Suggests it can work...    if I can screen grab the moment I'll post it here.

Update - client list count dropped, warning sign appeared, and rate counts started showing up:

Moments later it's back to showing blank rates...  no warning and more clients:

@GRB 

Viewing the web interface of the main deco shows real time data rates - so it's the app which is broken.

TP-Link support says "after checking ourdatabase, it is normal for the deco not show the speed of clienct" (typos, yes)

So anyone look for this information, while the app doesn't display them, try the web interface of your main deco.

Now, TP-Link - please fix the app