Do grip trainers work is a fair question, because grip strength is both a trainable quality and a measured health marker. The short answer is that squeezing a spring gripper builds crushing grip specifically, but it is a narrow slice of what grip means, and general lifting often trains grip more broadly than a dedicated gripper does.
What a gripper actually trains
A spring grip trainer builds crushing grip, the closing strength between fingers and palm, and it does improve that specific quality with progressive resistance. But grip has several components, pinch, support and crushing, and a gripper trains mainly the last, so do grip strengtheners work depends on which kind of grip you mean.
Grip as a measured standard
Grip strength is measured with a dynamometer, and there are published norms by age and sex, which is why it appears in health research as well as gyms. Reading your grip against those norms tells you where you sit; a gripper can move that number, but so can heavy deadlifts, carries and rows, which load the grip hard as a side effect.
When a gripper is worth it
Do grip trainers work well enough to bother is a training-economy question. If you already lift heavy, your grip is probably progressing without a gripper; if you want maximal crushing strength specifically, or you do not lift, a gripper is a cheap, effective tool for that narrow goal, used with progression like any other lift.
Questions people ask about do grip trainers work
Do grip trainers work?
A spring gripper builds crushing grip specifically and does improve it with progression, but it trains only one component of grip; heavy lifting often trains grip more broadly as a side effect.
Do grip strengtheners work for general strength?
They build crushing grip, which is narrow; for overall grip, heavy deadlifts, carries and rows load the grip hard and often progress it without a dedicated gripper.
How is grip strength measured?
With a hand dynamometer, against published norms by age and sex, which is why grip appears both in gyms and in health research as a marker.