Four ways to stop a bag turning into a cable knot, tried over a month of travel each, rotating through so I actually got a fair comparison rather than judging one on a single bad day.
The velcro roll is the cheapest option by a wide margin, and does the job of keeping cables from tangling with each other, but does nothing for the "which cable is which" problem once everything's rolled up identically.
The hard case is the bulkiest by far, and the one I'd leave at home for anything but a longer trip — but it's also the only option that survived being sat on in a rucksack without anything inside cracking, which matters more than I expected until it actually happened to the velcro roll's contents.
The magnetic clips on the bag strap turned out to be the dark horse. They don't hold much — one cable and a small dongle, realistically — but for the two things I reach for most on any given day, having them clipped somewhere I don't need to unzip anything to find has genuinely changed how often I dig through the whole bag.
Photos of each below — the magnetic clips won out in the end, mostly for speed rather than capacity, which wasn't the result I expected going in.