The voltage converter seems to work as advertised. The problem is that the included cord is for a European plug. To get around this, the supplier includes extremely cheap universal travel adapters, which are not safe, and possibly illegal (for example, try the phrase "Concern about the dangers of consumers using unsafe power adaptors" in your favorite search engine.) The travel adapters are un-shuttered, and a child could easily fit their small fingers into the holes, directly exposing them to 240 Volts.
Again, the device itself seems to work fine, and it should not be difficult for the supplier to source legal wall adapters.