They're nifty, but not necessary. Being a double-stack double-feed magazine with a nice, long, barely tapered cartridge, M1 Carbine magazines are some of the easiest to load by hand.
And like M1903 and M16/M4 stripper clips, the flimsy little metal tabs that retain the cartridges and get bent out of the way during loading tend to break off after a few use cycles, thus rendering the clip useless.
(Stripper clips that achieve retention by using a flat spring along the inner spine, like M14 and Mauser stripper clips, are significantly more robust and last a lot longer.)
I have some of the same Korean surplus ammo. The stripper clips come with the "spoon" built in. Just pull it out, slip it over the back of the magazine and push the cartridges in. (Takes a bit of practice to coordinate.)
The 10-round stripper clips came along after the adoption of the M2 Carbine and its 30-round magazines. Which is why you need one and a half 10-round clips to fill the earlier 15-round magazines. :-)
This Korean surplus ammo is very accurate, but some of it was rather corroded. Cleaned up, it shoots fine.