Bikepacking - a viable alternative to racks & panniers

Need to track down a shop in the Midlands that sells something like this though - a recce of Brum's bike shops has drawn a blank, it appears bike packing hasn't made it to the Midlands yet.

Discovered that the Alpkit factory is an hour's drive away so will probably go there. From reading the last 10 or so pages it appears though that some people haven't had good experiences with Alpkit ? Thinking of either the 3L Kowari or the 8-13L Koala