Product review (3 stars): Should do more.
It's usually my thing to be hard on devices that plug into smart phones for no real reason other than they can, but I see that the Foegelle stole my spotlight (although did a great job).  Really, I jumped on this before I realized it was such a simple device.  The price actually fooled me into thinking it could do more, like maybe help diagnose HVAC systems.  Instead, it measures temp and humidity and then calculates dewpoint and wet bulb for you, saving you a few quick calculations.

Honestly, using phones to try to get any real work done really, really irritates me.  So to play around with this is fine, but for the price, it should work stand alone.