Useful to have some of these plug conversions around if you have not got Figure-of-8 to US two pin leads, which are far more useful, for battery chargers etc. Not just for USA use but many other countries using the very ropey US two pin system, in my case when visiting the Philippines. Very basic but do their job okay. I prefer the use of a correct lead (usually available on Amazon cheaply) but would use these when using a plug with USB connection. I would not trust the voltage output of a two pin plug with USB socket.
Just got back from our annual trip to NYC, got these and put them round the hotel room and what ya know just like being at home with 5 uk power points...perfect! 5 was a great number for 2 mobile, straighteners, iPad, hairdryer, curling things etc etc etc