Good point. The eBay page says the unit is a SX8847. When I googled "SX8847 datasheet", the first match was the L9958 datasheet I linked to. I don't know why, I can't find any mention of SX8847 in the datasheet.
However, the description of the I/O interface on the eBay page matches the description in the datasheet, so does the block diagram. Also, another item I found on eBay that appears to be a rather similar board has a L9958 chip in the photo, see http://www.ebay.co.uk/itm/Arduino-240W-High-power-H-Bridge-Motor-Driver-Module-Smart-Car-Driver-/330817755465?pt=LH_DefaultDomain_0&hash=item4d06465949.
So I think it very likely that the unit I linked to is based on the L9958.