Its surprisingly common, the datasheet for it is ridiculous with all its bells and whistles - built in battery charging supporting external pass element, almost endless button combinations for events, apparently even has basic voice recognition for hands free dialing. As CSR only deal with manufacturers, not end users, and only provide ROM's, its a case of relying on those who have done a bit of hacking to change config. You might not even need to change anything - the modules I had used relatively quiet beeps for power up/down, and key presses, had Apt-X enabled by default, and the bluetooth name 'CSR8645'. Whilst I've changed some stuff, that wasn't' really necessary (only did it because I'd spent so long trying to work out how!).
Theres another thread that I just posted on with the method - beware, its lengthy and involves copying/pasting strings of hex values from one file to another..
Another reason its popular is the Apt-X which really does sound decent. But I think its mare marketing, because there are many flavours of that codec, bluetooth uses either standard Apt-x (really coudn't tell the difference between that and wired) or low-latency Apt-x. There's also a 'lossless' Apt-x which is used in industry, and I've seen some sites claiming that because their bluetooth headset/speaker uses Apt-X, its lossless - it ain't. But it does mean cheap modules have become popular, driving down prices.
I keep saying it but I'm thoroughly impressed with it. The commercial products in my price range (which is pretty damn low..) always had issues, poor sound quality, crap battery life, uncomfortable to wear etc.. it's one of the few times where 'DIY' pays off.