They do a good job keeping up with your mask.
This is a great product at a good price.  The only reason I didn't give it 5 stars is because it catches in my necklaces and I have broken one taking off the lanyard.  I think I could loosen the knob part, but then it is hanging so far down my back that I would probably catch it on something else.  I'm not sure how to improve the product except to make it shorter and change the placement, or even the use of, even having the tightener knob.
Rating: 4 stars