Production-related error or blemish on connectors and fiber optic cable I could find none. The plug locks on my devices a flawlessly. Whether PC, Blu-ray player, home cinema speakers, LCD TV or other equipment that I connect to it; I've never had transmission problems.
The cable is not too thin. 1mm equivalent to the standard core diameter of a Toslink cable, and come within 5 meters length for cables of this type also no attenuation problems due to the plastic used for the fiber-optic cable. So one has to worry that another cable could better convey the audio signal to the terminal than this; which can not happen at such transmission technology.
The thin cross-section only means precisely that the cable is protected from the outside less to shocks or sharp-edged than those with thicker shell. To me that is absolutely secondary, because I laid the cable exactly once between TV and boxes behind the cabinet, and then - if everything works properly - not touch them for years.