The 40 MAX Whirligig II is the best budget grenade for airsoft use according to Fox Green which he explains in this episode. This device features a patented locking/unlocking mechanism that requires no external accessories or complicated resetting, simply rotate to lock or unlock. It boasts high security when locked and a highly sensitive trigger in the unlocked state, functioning on both soft ground and cement (with a minimum trigger distance of 30-40cm on cement).  Despite its high strength and 200bb bomb storage capacity, the device is lightweight at only 280g.