Well, based on their own paid for report from the Univ. of Southhampton’s ISVR (never heard of them before this, but they seem to be a small univ. research group near the manufacturer)… Calmer is basically an approx. 5 db attenuation above 2k Hz. That’s it.
Now, how that could reduce distortion is totally unclear, and seems pretty unlikely, since your normal hearing range will well over 50 db of range. So… If you’re listening to headphones at a volume where a mere 5 db drop is the make or break for hearing distortion - I’d say you’ve got way bigger problems by listening to anything that loud.
“Reduces stress trigger frequencies without muffling sound” seems like total “you can’t prove it” marketing copy. It’s not like there are specific “stress trigger” frequencies in the human ear. As for not “muffling”… Sure, a 5db drop at 2k Hz and above, once you’re acclimated to the curve (a few minutes) won’t sound muffling. Just like listening to your favorite album on your car’s crummy speakers doesn’t sound any less great once you’re used to it.
So basically- they are almost do nothing silicone ear plugs for $26 USD. Meh… Save the money for a take out meal, and just turn your headphones down a skosh. — And once COVID-19 is behind us, buy a pair of ETY Plugs ER20XS for half that amount, and do your ears some real protection at the next loud show you go to.