This item shipped and arrived quickly and in good condition.
To describe it, it's about 3 by 2 cm. The bottom end fits over the firewire dock in the speaker system, while the other end is a firewire connection that's just as wide as the end of the charging cable that comes with the iDevice. This means that you can easily use the iDevice in its case and dock again, while still charging the device (if your dock allowed for that in the first place). It seems to be less cumbersome if you put this connecter into the iDevice first, then put the whole thing on the dock, but that's just been my experience. I'm very happy with this purchase so far.
Update (June 2012): Shortly after buying this connector it stopped working. I realized that one of its seams had split. I wrote to the seller, explained the problem, and within several days had a new connector and an envelope with which I could send back the broken one. This was at no cost to me. I've been happy with the new connector and am very impressed with the customer service I received.