Pull the pin and let the propane do the rest. When Airsoft's Tornado Impact Grenades detonate, they scatter over 200 plastic 6mm pellets in all 3 dimensions under which your enemies might try to take cover. This means that unless they are cowering under a table like a wussy lapdog whose default setting is to shake like someone put a quarter in it, they're probably going to take a hit.
Tornado Impact Grenades are reusable with reloads of BBs and gas, and have been designed to last for "gazillions of throws!" That's a direct quote from the manufacturer. I have serious doubts about its validity. Unfortunately what I do not have are the patience and the math skills to count to a gazillion, so I'm not sure I can call them on it.