The Creative Bluetooth Audio BT-D5 is an iDevice dongle which comes included with the Creative ZiiSound D5. As the D5 caters to the upper-end of the listening experience, the dongle is supposed to improve the wireless transmission quality using the aptX codec. I don't fully understand the technical aspects, but I believe it does this by compressing the information, such that more can eventually be sent over to the speakers. The result? More information, and hence better sound quality.
Connectivity - this is excellent and easy. All you do is plug it into your iDevice, press the connect button (there is only one button on it anyway), and viola, you are paired. The connection is excellent, with no dropping or stuttering in play.
Sound quality - there is a noticeable difference with the dongle on compared to wireless Bluetooth transmission alone. In my ZiiSound review, I noted that the bass was quite flat. The BT-D5 mitigates this somewhat. In addition, the treble sounds a lot fuller, while keeping sharp, which is really important to me as I listen to a fair bit of classical music.
Battery life - this is the main downside of the dongle. It appears to be a major drain - my Nano normally has a battery life of 24 hours (playback). With the dongle attached, playback time was reduced to six hours. I have yet to test fully the effect on my iPhone (battery life is just too precious), but having it attached for about an hour resulted in 15% drop in battery. On the plus side, you can dock the BT-D5 for simultaneous charging, although I think that that defeats the point of wireless... might as well use an AUX cable.
Conclusion - if you have Bluetooth speakers, this is definitely something you should consider, especially for home listening where chargers are handy. It comes at a price though, averaging about £40.