H i have a BT smart Hub 2 with 3 black BT disks too. When first sent up it was all working ok but has gone downhill lately. If you move around the house themobile items do not change to the nearest disk. I live in a 4 bedroom house with a conservatory and a Garden room in the garden 30 feet from the back of the house. What if any would improve my WiFi around my house and garden. Also can i buy more than 3 units if i want too. By the way i get 70Mbpsinto the house.