Engine stop leak.

I was in super cheap auto the other day and came across this stuff called wynns engine stop leak. It is supposed to add new life to old seal/gaskets and prevent your engine from leaking oil.
Has anybody ever used this stuff or anything similar?
And if so does it work ? and is there any draw backs to using this type of product?
Wynn's Australia - Retail Products

I have used it in the past on a Rally Car to get the car to the finish line, yes it does work as long as the leak is from a seal as it softens the rubber.

wynn's products are good stuff its what we sell at work (i work in a motor factor) most of the trade use wynn's stuff