How safe are electric faucet water heater?
I would consider them unsafe for the U.S. market for 2 possibly 3 reasons. First it is not U.L. listed this means it has not passed normal testing for being used in the U.S. 
Next, it comes with a different style plug so the first thing you would do to use it is modify it electrically so you could use it.
Another item is it has metric plumbing, this may not be a big safety thing but you may have trouble adapting this to your parents plumbing. If a failure it may just leak or flood an area of the home.
With these issues I would check a plumbing store or big box store they may have something similar that probably will cost more but would be listed for use here thus be legal. I was thinking the country plugs this comes with are on a different standard than we are so I found the voltage is 220 so you will probably need that brought to the location as most outlets in North America are 120v.