Product is simple and easy to use - just plug it into the wall and plug your US adapter or plug into the back. There are no switches, sliders or knobs to fiddle with.
However, it's a little bulky and heavy for its size - perhaps a little larger than the US adapter you might be plugging into it. But it has a strong grip, so the combined adapters don't fall out of the wall.
The weight means P+P is expensive.
Update Jan 2009: We found that this doesn't work well with a USA clock, since it doesn't convert the UK's 50Hz mains frequency to the USA's 60Hz frequency - so the clock loses 10mins every hour!