It's almost surely some kind of load cell, which uses strain gauges in a bridge configuration as in Andy's answer.
It's not obvious to me what the most appropriate shape would be to fit into that case, have axial load attachment points, and have appropriate strength and sensitivity (it has to bend for there to be strain to measure, but not so much there is danger of permanent deformation (past the yield point in ME terms).
The S shape would work in tension as well as compression (opposite polarity output) but that type you linked too seems too insensitive for your application. It's possible the construction is similar inside, just much thinner metal.
Try search terms such as tension micro load cell (and pull load cell for the ESL results). Also "axial load cell".
The main disadvantage with tearing down the cheap sensor is that the output voltage won't be calibrated, which does not strike me as that big a deal if you have some reference weights to hang off of it.