I have been using the 665 for over a month - it has great sound quality for me, and for the listener on the other end. It stays in my ear better than the headsets that require that you use the over-ear piece - I have long hair and this earpiece is the ONLY ONE that I don't have to use 2 hands to keep in my ear. My only complaint is the charging component. For me, when you have to use 2 pieces to charge something - it increases the chances for losing one of the pieces. The 665 requires that you put the headset into this holder; and the holder plugs into one of 3 chargers that you receive with the headset. I DO like the holder because it HAS A CLIP on it - which I use quite often (and I think it's great that they supply a charger for car and USB connection as well as electrical outlet)