Product review (5 stars): If you like knowing the pH of liquids...
I bought one of these for the sake of satiating some curious tendencies about what I ingest.  Wine, Beer, Whiskey, Juices, Water from different sources, Milk, etc.  But I especially was curious to see if a Sawyer Filter I purchased for hiking/camping effected the pH of field water (it doesn't).

When you get this device you will have to calibrate it - very simple but the instructions are a little hard to make sense of.  In any case they provided 2 packets of calibration salts:  One will stabilize the pH of water at 4.00 and the other at 6.86.  They provide enough salt to create a 250mL sample but I only needed half of that in an 8oz glass.

Assuming you use the entire contents of the 4.00pH packet...[Pro-Tip: measure out half of the contents and 125mL of water and store the remaining salt in a ziplock bag with the air removed]
Step 1: Pour the contents of the packet into a glass container - preferably taller than it is wide (think of a Collins glass)
Step 2: Pour in 250mL of water and stir until dissolved
Step 3: Turn on the device and lower it into the solution.  There are minimum and maximum immersion marks on the reader, steady it somewhere between
Step 4: With the device sitting in the solution, use the provided flat-head screwdriver to turn the screw on the back of the device left/right until the reading equals 4.0.
Step 5: If you want to ensure calibration was successful, perform the same steps with the 6.86 solution.  Your device should read 6.9 without you having to calibrate further.

That's it, its easy and pretty accurate, the only fault I've found is that the calibration screw on the back is a bit sensitive.  I haven't had to re-calibrate in the few days that I've had it, but I'll be keeping my eye on it.

5 stars because it's hard to rate a product like this - either it works as prescribed, or it doesn't.