Has anyone tried one of these to prepare for higher altitude events? I have not found reference to them on any cycling sites, but they seem to be popular for other pursuits, at least by those who have reviewed them.

https://www.trainingmask.com/trainin...SAAEgLI8fD_BwE

A straw is cheaper.

Gimmick.

Edit to add: they're good for scaring children who've seen Hannibal Lecter movies though.

There is a lot more to exchanging CO2 for O2 at altitude that restricting airflow at lower altitudes won't make up for.

Gimmick.

Also, lookup altitude sleep tents instead if this is a serious thing you want to do.