So it is perhaps not so surprising that people stick to a rucksack (which can be used in other contexts as well, unlike a saddlebag).
Right tool for the job though, saddle bag for the saddle, panniers for the pannier rack, rucksack for walking or where there is no other choice.
You have to admit that flexibility means they are a compromise on the bike and made doubly uncomfortable on a road bike due to rider position.
I do have a Carradice but they are expensive (compared to a rucksack)
Depends on the rucksack, the price overlap between tiso's range or rucksacks and carradice's range of saddle bags is very small. Tiso's cheap rucksacks start about the same level as the larger saddlebags.
But to each their own.