Ek Mukhi Rudraksha Can Anyone Throw Some Light On Ek Mukhi Rudraksha?

Can anyone throw some light on ek mukhi rudraksha? - ek mukhi rudraksha

A friend of mine today at Hardwar (India) on the tour and piligrimage wants to buy in a store that is managed by the Govt. This is expensive. He says he does so for good luck.