I bought a Mule a few years back and it was just way too small for my modest needs. Sold it and bought a Deuter Bike bag, on reccomendation from CG on here.
It’s been bloody brilliant – I like to take my dslr with me, as well as lunch, tools, 3L bladder etc. If you just havea a few tools, there are compression straps to stop the thing flapping about.
Also has a built in rain cover (useful for sitting on!) and a helmet carrier.
Build quality is as good as anything else I’ve had – better than most and it’s still going strong.