550 o2 sensors for $16?

I saw the following on ebay , anyone know if these generic sensors really work?

If the link fails, use ebay search engine with " ferrari 550 sensor"

http://cgi.ebay.com/ebaymotors/OXYGEN-SENSOR-ferrari-550-97-02-01-00-99-98-1997-2002_W0QQcmdZViewItemQQcategoryZ42610QQihZ014QQitemZ330143273723QQrdZ1QQsspagenameZWD1V

Regards,
Ron