SodaStream, for the original intent of producing cheap soda at home (much like the old soda fountain).
Turned out that the expensive flavourings cost as much (actually more) as Real soda in the long run. Buying the Store Brands (88¢) Soda is cheaper, almost half the cost of SodaStream.
Plus, it turns out that all the normal flavours of the SodaStream brand are DIET (aspartame) crap. They fraudulently imply that their flavour isn't 'diet' because some of their flavours being labeled 'Diet' by use of a different artificial sweetener.
The "Naturally Sparkling" flavour uses real Sugar but is 33% more expensive and, all but impossible to find. To order it direct doubles the cost because of the shipping charges
I think it may take about 10 years to recover the cost of the base unit (69.99$US) by just making sodawater.