This is an interesting device. One part of me wants to point out that for emergency self defence use a standard bottle cap will be more than adequate. The “sip-nipple” type caps will concentrate the force on a smaller area.
On the other hand, this product does raise the user’s awareness that a bottle in hand can be used for defensive purposes against an aggressor. There is also a nagging part of my mind that insists this thing might be adaptable to applications other than just on bottles.
I see quite a few joggers carrying bottles such as these.
The hand grip and the fact that they tend to be carried in hand rather than worn on a belt gives them good defensive potential and I wonder how many joggers are aware of this fact.
Even without a fancy cap and design a bottle of water can be a good weapon. Water is incompressible and has weight. A filled half litre bottle will add an extra pound to your strike, which can be concentrated into the small hard area of the cap using the Kongo techniques in my book. The surface of the bottle can fend off a knife edge. It may damage the bottle but may buy you enough time to escape. A bottle can also be used as a missile to distract a foe long enough to counter attack or escape.