Yes, of course it's safe to wear pinhole glasses. And you should know how they make improve your vision. The moment you put on pinhole glasses you will notice instant clarity and focused vision. By blocking peripheral rays, and only letting into the eye those rays which pass through the central portion of the pupil, any refractive error in the lens or cornea is not noticed as much. The pupil may be wide open, but only the central portion is receiving light. The improvement in visual acuity can be striking. Pinholes can be used as Sunglasses, computer glasses, and Myopia Prevention Glasses and for those with Cataracts or Corneal Damage. So there is no worry about the safety of using them. Just have a try.
Yes, they are safe to wear. Equivalent to the principle of camera lens that small aperture can increase the depth of field range, they can improve the vision. They can prevent you from increasing your prescription, but not cure your short sighted eyes. It belongs to the health care products. If you want to have one, you can go to the foreign online store and have a look.