[Closed] Anyone use a power meter for training?

I have a friend who has entered the [url= http://www.davelloydmegachallenge.com/default.aspx?id=4 ] Dave Lloyd Mega Challenge [/url] and is training like a man possesed, he has lent me a book about training with a power meter, now is it the cynic in me that thinks if i swap 'powe meter' for 'heart rate monitor', its just something i read 15 years ago, or are power meters a more accurate/detailed way of training?