I have a couple of Billingham bags, one I don't know how many years I've had it but it's a long time. I've had a replacement zip and shoulder strap a year or two ago. The bag cost a lot 15-20 years ago. It still protects my gear, it still holds it shape. Someone I know very well has had a load of cheap bags, they still can't see why I would spend double and more on a Billingham. Not only does a Billingham last forever, it does the job better.
His bags are flimsy, so much so that if packed with gear they offer little support. I've seen lenses roll out when the bag is put down.
Seldom have I ever seen anything that costs the least be the cheaper option on any product.
I never buy cheap, I'm happy to pay for a name, often getting that name has taken years of building quality gear I hope they value their name and reputation and will not cut enough corners to compromise it.
It can take little time of use to find out why something is half the price of something that looked very similar but cost more.