Essentially this device hooks up to you (probably around your chest) and monitors your breath. Then, if you are breathing faster than 10 breaths per minute (the therapeutic zone) it creates a custom melody that will help you slow your breathing rate.
It plays the melody through the headphones, you just try and sync up your breathing to it, and after you do, your blood pressure should drop as that apparently causes your vessels to dilate. So, finally, music has done something good for your body, just be sure not to crank it up too loud, no sense lowering your blood pressure as you destroy your hearing.
If you have blood pressure problems, finding another way to control it and lower your blood pressure is a far better idea, one idea is meditation. However, if you still feel this is the best option for you it costs $290 and that alone ought to make you sign up for those meditation classes.