What is the diffence between BT Mini Connection Kit and BT Broadband Extender Flex 600 & 1000? Both Ethernet via mains but do they also extend Wi-fi coverage?
None of them extend wifi range, only Ethernet connections.
For wifi you need https://shop.bt.com/products/bt-mini-wi-fi-home-hotspot-600-kit-084288-BVFF.html
These create a new wifi network, and also extend Ethernet connections.