One important thing about gas checks in handgun applications is that they're usually not needed so long as the bullet alloy is a good one. You don't really need them for any 44 magnum applications, for example. If you get much over, say 1500fps, then they may become necessary. Before buying gas checked bullets try bullets that are not gas checked and see if you get excessive lead fouling.
It would be helpful to know what you plan to shoot.
In rifles, the gas checks are more important because you're shooting around 1800-2000fps.
The alternative definition for gas check is when we excuse ourselves and go outdoors to break wind. It's the polite thing to do.
