Product review (5 stars): it works
Overall, I like it. I'm not sure how to get an absolute verification that it is giving me the right number, and anyway, close enough is good enough for a science which is perhaps not entirely precise.

It seems to take awhile to kick in. Say I'm indoors and the humidity is 45%. I hear from Google that the humidity outdoors is 90% (it's raining). I take it outdoors to a sheltered location. It still reads 45%. I come back an hour later, it reads 89%, which is close enough for a commercial product.