Product review (5 stars): Great multi purpose tool
After reading through some of the other reviews, it occurred to me that people may have overly high expectations of what to expect from a cheap indoor/outdoor thermometer/hygrometer so I took a chance with this and, so far, have not been disappointed.  The display is large, clear and straightforward.  The main unit only has three buttons: Two to display the recorded max/min values and one to switch between Fahrenheit and Celsius.  I love it!  The secondary unit has NO buttons: just stick it somewhere and forget about it.  Mine is in my basement out of the sunlight.  If either unit receives sunlight, your measurements will be off.  If you stick your secondary unit in an area with little air flow, your measurements will be off.  There are a lot of variables at play when deciding where to stick these things.  If your measurements seem wildly off, do some research and make sure you've got everything placed correctly.  I'm very pleased with the accuracy I'm getting from both units and am glad I made the purchase.

I'd caution against using rechargeable batteries in either unit.  Due to some science stuff that you can look up on your own if you're interested, these low-power units will probably burn through rechargeables pretty quickly.  I'd guess that some of the reviewers that had a hard time with battery life would probably benefit from using disposable batteries.  The same rule applies for any low power constant draw device, like an alarm clock or smoke detector.

I'll be sure to update this post if I have any negative experiences with the unit!