The challenge is that while you can make a strain gauge out of just about anything, making them repeatable over temperature, humidity (in the case of hygroscopic materials, like PCB FR4) and repeated flexing is where it gets difficult.<p>For this, while I'm sure it works, if the humidity and/or temperature changes, the same deflection will result in different readings.<p>If you can calibrate it <i>immediately</i> before each use, or you don't care about absolute values, this is a completely valid option.<p>"Real" strain gauges generally use a constantan resistive element to deal with the temperature variability, deposited on a plastic carrier film (typically polyimide). The film elements then get glued to the stress sensing member. They're fairly inexpensive too.