The safety isn't too sturdy, if it sticks, a good solid twist, the safety fails, and the flare fires.
It's enough to stop it from firing accidentally, but the first dozen or so of the newest ones I fired I couldn't actually figure out how the safety worked, I just twisted hard and it fired.
Don't know if anyone's thrown the "new" t-flashes, but they seem to be safer then the old ones... the tubes are sturdier and wrapped in plastic, they blow out the ends, rather then exploding in the centre... makes spotting duds harder, but in the even one ever went off in your hand, you'd probably have a better chance of walking away with your fingers...