Those Flash packs look good, but for someone looking to replace seat bag and the rest and have one consolidated place for tools, tubes, and clothing, I'm not sure how it would work.
The Flash has an internal pocket system - one big sleeve against your back big enough for a hydration bladder, and on the "front" of that sleeve there are a number of pockets. They're not the easiest to access, especially when you've got other stuff in the bag, but they hold things in place. I have a pump, multitool, spare tube, cell phone, wallet and keys all stowed in the various inside pockets for my commute, with clothes and lunch in the main compartment.
I do wish the pack had a few external pockets but like I said, for $30 I'm pretty happy.