Isn't the child afraid of the Baby-Vac?

It depends on the child. Some of them are afraid at first, but later they get used to it. Some children even try to use it alone, but it's better if the parents use the apparatus.

Is it necessary to use a vacuum cleaner/hoover?

The secretion can not be removed from the nasal cavities, unless you have strong continuous suction.

The device is tested by internationally recognized bodies