I think those great value products are not in fact produced by Walmart. It's the same product from the same company, just lower priced to appeal to price conscious customers.
Thats exactly what those are. I worked for Reynolds Consumer a while back and the same aluminum foil goes into the brand box as well as the private label box.
The foil might be the same, but that doesn't mean everything is. I've had generic raisin bran cereal that was clearly Kellogg's in a different box, excpet that 1 out of 100 boxes had a slightly different flavor that wouldn't have passed Kellogg's quality controls but since still food safe (so I assume) the generic boxes got it. Of course when doing a private labor you can specify the higher quality controls, but that comes at a higher price. Most of the time Kellogg's is going to make the same cereal either way so nobody can tell the difference, but when something goes off in the process the cheaper generics get it.
My knowledge of foil suggests there isn't anything Reynolds could to that would reduce quality that would still be good enough to ship.
I dunno how it is these days, but the store brand cocoa pebbles used to not taste like chocolate at all, and would fail to turn the milk into chocolate milk like the real ones did. Other cereals had similar problems. A common issue was that the store brand was consistently, noticeably stale, while the name brand almost never was.