If it's a factory magazine, new, it's most likely perfect. Used, you take a chance. Offbrand, almost never - only if you have found others who have tested it for you. I only will carry known, matching brand magazines I have used. All others need to prove themselves.
It's like changing your oil - a cheap filter will save $2, but you can't ever drive one long enough for the savings to buy you an engine rebuild. In this case, will an inexpensive magazine that fails to function be worth it when you need it?
Some like the adventure of shopping for cheap, but I've learned it's like a spouse - you want a trusted, high quality friend known for proper conduct, not a cheap fling that could endanger you personally.
There are things in life where it's dangerous to cut corners.