Seems to be a solution in search of a problem.
Why would you need them?
Hunting? If you miss with 8 rounds, maybe you shouldn't hunt.
At the range?
Going to war? then you use a cartridge belt, but WW2 and Korea are over.
Now I am sure the product is well made so not putting down that aspect.
Reminds me of those 30, 40, 50 rd mags for AK's and SKS's
Or those "Scout rifle" scopes
Oh by the way, you can still find GI stock pouches for the carbine.