On a serious note, I've just fitted a Givi 3d603 and am very pleased with it. I just wanted somewhere for wallet/glasses/camera/phone, so small is good. The tanklock system is good too. Being small it doesn't obscure my satnav or clocks.
I was going to go for the 3D604 bag, but was concerned that it would obscure my Sat Nav which is mounted on the bars.