This item works well for me with a Sony Ericsson k800i.
Good:
-Battery life very good
-Good small size and very discreet, does not get in your way during driving and is not visible from the street if the sun visor is up.
-Sound quality pretty good on the move in a car. Sometimes you need to repeat yourself.
Bad:
-Cannot get voice dialing to work via the HCB-100. I have recorded the voice tag via the phone and the HCB-100, it does work with my phone.
-The mains charger is a CST-61, and not a CST-60, which is the current type of socket on most new SE phones. The 61 charger does work with it, but it's not that secure, I expect the lug to connect it will break soon.