Product review (3 stars): A helpful device
Living on the Central Coast of California, humidity and mold are always issues. This sensor lives in our kitchen and is a good indicator that we should probably invest in a dehumidifier since it almost always reads in the red zone except for overnight when the house temperature drops. We didn't bother setting alerts since it's pretty much always in the humidity range we expect: 65-75%. It will be interesting to see how much the dehumidifier helps. I would also say it is consistent with the humidity sensor on our ecobee thermostat.  They run within +/-3% points of each other so that also inspires confidence. Ultimately this device hasn't told me anything I don't know: there's simply too much moisture in the indoor air of our house.

One major complaint, no way to plug this in. It eats batteries pretty regularly, even high capacity rechargables, so it's something to watch. Not a deal breaker but an annoyance nonetheless. Other minor quibbles include the fact that the display does not light up at night; it seems like some lume would not have been all that difficult to incorporate.