The Official wireless headset is basically a slightly bigger than average Bluetooth headset with Xbox features. It lets you connect (once paired up) to the Xbox 360 in place of the wired headset you get as part of the standard package with the console.
The item comes with another 3 sizes of earpiece, allowing you to better fit it to your ear, though I found none of these fitted perfectly (but then perhaps I have funny ears!). The looped bit of plastic holds the headset in place well, though.
After charging, something you can do through the 360's USB port, the device was very easily connected to the console. The first time I tried, though, it went to channel 2 instead of the first one for player 1. Turning it off and on solved this. The sound in multiplayer was fairly clear on both sides (microphone and earphone) but a constant clicking kept annoying me.
I'm sure it was just interference, but it did cause a bit of a problem and I ended up going back to the trusty headset in the end.
I've since used this as a bluetooth headset for my iPhone and it actually works pretty well, even better than with the Xbox. It also works perfectly with the PS3, which seems a tad ironic.