Time was fairly accurate,ranging between 25-35 seconds among the ten hourglasses.
The biggest flaw is that only one side of the hourglass is flat, rendering it much less useful. If you have it standing up, you have to flip it once, wait 30 seconds for the sand to transfer, and then you are ready to use it. The alternative is to have the hourglass lay on its side but then they are prone to roll. Not bad for the novelty price point, but would be significantly better if both sides were flat and allowed the hour glass to stand up on either side.