A lid is a friction problem wearing a costume. The glass is smooth, the metal is smooth, and your hand is the only part of the system designed for something else.
What it does
The band wraps the lid and gives your hand something to hold. Because the grip material is wider than your palm, the force spreads out instead of concentrating on one sore spot.
What it does not do
It does not loosen a lid that has been sealed by vacuum after a hot fill. For those, run the lid under warm water for thirty seconds first, then use the band.
Care
Rinse and air dry. It is not dishwasher safe — the grip compound softens above 70°C.