This travel adapter set consists of a main unit into which you plug an American plug and 13 attachable units that allow you to plug into any socket in the world. There are two units for US sockets, one grounded and the other ungrounded, that is, two pronged old style plugs. The main unit also has USB A socket for charging phones and a USB C socket. Phone charging works fine, but is a bit slow. What makes this unit safe is that it has the extra grounding prong for most of the attachable units. That also means that it needs a lot of attachable units. They come in a cardboard case that are labeled for the countries in which they work--be careful not to get them confused. So, if you know where you are going, as you usually do, you can just take the units that work for where you will be. If you take multiple attachable units, you should know that it is very easy to take out and put another in. Most countries in Europe use two prongs to carry electricity, but the third ground prong differs in different countries. So, you pay a price in safety for the convenience of using a an adapter that is ungrounded but works in multiple countries, and you pay a price in convenience when you use this set, where you use a different adapter for different countries. Probably, you should go with safety and use this set. You can also use the US units at home to charge your phone. I wish the phone charger were faster.