Product review (3 stars): Not sure it's accurate...
There's not much to review. It measures the relative humidity and temperature. There's a nice graph at the bottom that displays optimal humidity and the effects of too high or too low humidity.

I'm not sure this is accurate. Since purchasing a dehumidifier with a temperature gauge, it's routinely a much different measurement than the dehumidifier. Currently, my dehumidifier shows 41% relative humidity and the Vicks Health Check Monitor shows 48% relative humidity.

It's nice because it's independent of a humidifier or dehumidifier, so you don't have to be running something to find out what the relative humidity is and can turn the devices on when the Vicks Health Check Monitor gives you an idea that you're outside of optimal humidity.

But again, don't rely on this as totally accurate, which is important to note because living outside of optimal humidity can have deleterious health effects.