Those sensors work, but they don't give you a very accurate weight, that is not their purpose.
For more accurate weighing, usually use a device with an aluminum bar with a load cell bonded to it and a hole drilled to weaken it and increase the deflection to measurable levels. You then need an amplifier circuit and adc.
if you want to get relative high-Precision result, i suggest you use the load cell weight sensor and amplifier. i do not know your mearing range , maybe this would work:Weight Sensor Kit- 3KG