I ordered the 520 old model but the wrong model was delivered by the nonAmazon merchant and I returned them after I received them(I had to buy 3 packages just to save shipping fee) With this 820 model, it is sold by Amazon directly so it is great as I got it shipped free thanks to Amazon. The unit is VERY comfortable and good sound quality. I love its behind the ears design b/c it does not hurt my ears like other the traditional over head kind