Watch De-magnetiser?

My Oris is gaining 15 seconds a day, and the last time I took it into the shop they said I'd got it magnetised.... And promptly de-magnetised it for me...

I'm assuming its in the same state again now, and was idly looking on ebay and you can pick up a watch de-magnetiser from 15 quid up....

Anyone have any experience of these things? Do they work?

Taken from Wikipedia's fine article on de-gaussing mixed ferrous metals objects......

"Sudden sharp impacts in the range of 200-256KG/MS from iron objects has the effect of de-magnetising 78.6% of any known magnetic field.....we recommend and thoroughly guarantee that if you whack your watch with a fucking big hammer, you will never have to worry about the time-keeping accuracy factor again"

Hope that helps Bryn

Thanks Bill.. May be an option