The Ultegra 6800 rear hub is a nice value in a durable and reliable hub. The ball bearing design is easily serviced a digital adjustment system borrowed from Dura-Ace makes adjustment easier than ever. The excellent labyrinth seals keep out dirt better than most sealed bearing hubs.
The 6800 rear hub is compatible with all modern Shimano/SRAM cassettes up to 11-speed. The hub includes a spacer that is employed when using a 10,9 or 8 speed cassettes. When using most Shimano 10-speed cassettes you will want to use the very thin spacer included with the cassette as well as the spacer included with the hub.