I have used CS50 for a long time and I got 510S as a replacement. After trying 510S for a few days, I went back to CS50:Pros:Works for both my landline and cell phone at the same time, I realy like this.Good sound quality.Cons:Compares with CS50, I got much shorter range. This is the deciding factor that I switched back to CS50. Had it been a class 1 (100M range), I would have kept it and given it five stars.If you do not require a work range more than a couple of meters, this is the right product for you.