This customer's feedback is quite a common reaction with these string tension measurement devices. While these devices are intended to give you quantifiable measurements, they will not tell you the tension at which the racquet was strung (which is why I put extra emphasis on "proper use" of the device, which can be very subjective).
These measurement devices are merely to give you a reading of "stringbed stiffness," not "reference tension" which is the tension you set on your stringing machine. Stringbed stiffness will always be lower than your reference number.
As far as the difference between the reviewer's tension meter and his friend's, there are many many factors that can lead to this difference.
The main goal of these devices is so that a player can identify tension loss over the life of the string because the strings are constantly losing tension.
I hope this is helpful, as I know it can be very subjective and difficult to explain.
TW Customer Service.