How about a tape measure
Seriously, I have one of the beaded chain versions & it works quite well. I adjusted it when I first got it to make sure it was accurate - only modification I made was to paint the appropriate marker bead for HS red to make it easier to see.
The whole stretching argument doesn't make much sense to me. The only way to make a material stretch enough that it results in permanent elongation is to apply opposing (pulling) forces sufficient to overcome the material's yield point or elastic limit. What was their explanation for the cause?