Product review (3 stars): Neat idea, but check your accuracy first!
The idea is great. Unfortunately, the accuracy is a little low. I bought two of these, and discovered they read differently when in the same place. To test them, I put them in a sealed plastic container with a salt solution. This should always report 75% humidity. One read 76% and the other read 81%. I called Planet Waves, and they said the acceptable tolerance is 5%, and since 6% is close to 5%, reading 81% is within tolerance. That's disappointing since there's no way to calibrate it. At least the app lets you adjust thresholds, so I just set the thresholds higher for that unit. Regardless the idea is great. I can keep track of the humidity in my cases and be alerted when it gets out of range. If I'm not playing for a while it's nice to be notified when I need to replace my humidifier. But with the poor accuracy, I can only give it 3 stars.