The bluetooth upgrade is a must-have imho. Very easy to pair, sound is very good (I didn't notice any difference in sound quality) and the mic is extremely good. Maybe even better than in the original cable. Changing volume and skipping songs needs a little getting used to, but after an hour you do it without thinking. A full charge is good for around 3~3.5 hours of active useage, and it has earhooks so the earpieces do not fall out of your ears. Funny thing it they (by accident) sent me the BT 4.1 module instead of the updated 4.2, at least it said 4.1 in the manual. Anyway, a great upgrade if you have KZ headphones. I use mine every day and must say I am very happy with it.