This new formula does NOT burn the inside of mouth, it has a crisp, tingly feeling while I am rinsing, and it remains effective for a very long time after just one use! As the unit will often grab back the call if you are within 30-40 feet of the car! There’s not really an instruction book for assembly, but a diagram breakdown. I also know that BOSE has a more-or-less "no questions asked" policy on returns and exchanges—or at least they did years ago when I had to replace my noice canceling headphones several times over a period of like five years. Sound quality of both the mic and the headphones speakers are very good and the headset is comfortable. I ordered a size 9, the next available size up (based on the reviews). I received the product and when I tried it on I found that it was a bit big in the chest area, but that might just be me. If you have more money, shoot for the M40x or m50x if you want to walk around or need better quality. The sound quality is excellent, the 360 feature is nice, you dont have to worry what direction the speaker is facing. Overall I recommend!