In reply to jk25002:
I've had a Gourdon for well over a decade. It's a simple design that costs very little and does the job of keeping things dry very well, but it's not my first choice for cycle commuting with. I think I've used it for over night bikepacks in the past when I had less on the bike options, but for loading up and getting out the house quickly in the morning, I find it not nearly as good as the Osprey bags in terms of useful features and so on.
I guess what you need to carry makes a big difference! A pump, tube, tools, waterproof and hydration bladder will work fine with many small light bags, but add a laptop, lunch box, a file with papers in them for work or uni, pens, work ID and keys, at least clean undies but for some people work trousers, shirt, even shoes and a towel etc. then a very different type of bag is going to be worth it.