In all honesty I can't tell if it's safe to use, or a Darwin Award device.
Safe to use? For very loose definitions of "safe" and "use", maybe, provided you're using one hand, not grounded, and willing to ignore burns, sudden involuntary muscle contractions, nerve damage, etc.
If you want to try for the award, simply use one finger from each hand. No grounding required!
It's the volts that jolts, but the mils that kills.
Sing it, brother!
Put enough current through your heart and lungs (it doesn't take much), and you're outta here.
I had a professor who was fond of claiming that you could kill yourself with a D-cell. He recommended sanding the skin off the inside of your wrists, rubbing lots of salt into the wounds to improve conductivity, then holding the battery so that the positive terminal contacted one wrist and the negative terminal the other.
Who knows, it might even work. But you'd have to be
really determined.