As a former 2 1/2 pack a day smoker I can vouch for it ,
it does work .

It won't make you "sonically invisible" , but it does reduce the hacking noise a lot . A lot also depends on the original volume of the cough and how you pack in the cotton balls . Too few and it doesn't help , too many and it won't work . You have to change them frequently , so finding the right number of cotton balls , and placement inside , takes a little experimenting .

When it's working well I think it confuses the deer more than anything else , it makes you sound further away . I've still seen them become alert , but they relax far more quickly since they think you aren't close .

I don't hunt without mine .