How "good" are emergency hand crank chargers for mobile ?

[Techie#1]

How "good" are emergency hand crank chargers for mobile/moto defy...like this one >Emergency Mobile Charger : ROTO (Mechanical Charger) | eBay .Want to get 1 if this stuff works?...any1 already brought1 or anything similar?

 

[cyclops13]

I have used LED torches which work like the same way.
So it should work, but might take a long time to charge.