The service from the seller was excellent - the item arrived swiftly.
However, the battery itself is not a genuine Sony Ericsson item. The battery in the photo shows the 'real deal', however the one I was actually sent was a fake and of extremely poor quality. For starters, it did not have the Sony Ericsson hologram sticker. The battery case was made of silver paper rather than the solid aluminium casing that the genuine battery would have had. The print quality on the label was very poor (nothing like the genuine one) and, if that wasn't enough to convince me that it wasn't a genuine battery, one marking at the bottom of the label read "Made in Japan" and the one right next to it read "Fabrique en Chine".
These points would have been neither here nor there had the battery actually been any good, but it wasn't. The label read 930mAh (same as the original) but I very much doubt it was in fact any more than 400mAh. After a full charge, the battery would go flat within 9 hours or so - i.e. not even enough to last a full day.
Far better in my opinion to spend a little extra and buy a 'proper' battery direct from Sony Ericsson.