Oh boy! First post, but I hear me out. I’m a respiratory therapist by profession. For those not living in North America, or unaware of the profession, we deal with all breathing related issues from diagnostic to therapeutic, including placing breathing tubes, putting patients on ventilators etc.
Essentially this device if making you breather against a resistance. When you breathe in, this resistance hinders you from breathing in, so you use more diaphragm and other accessory muscles to breathe in. When exhaling you are breathing against a resistance, which a) limits the outward flow and primarily helps open up your lungs and b) again you have to use higher muscular effort to breathe out.
You could do the same by breathing in through a straw or blowing a balloon. This device probably has some flow measuring device which they use to tell you what your flows and volumes are, but do you really need those numbers, I doubt it’s as accurate as pulmonary diagnostics.
And this would do nothing for asthma. Asthma and COPD are very, very different .