A bottle of helium has been enough with us for 6 foil balloons with 45cm diameter.
But a bit trickier designed the filling of normal balloons. Because here the opening for injecting or pouring the air or helium is slightly larger than the width of the supplied here filler neck. Therefore, the helium escaping during injection immediately at the sides of the filler neck. Remedy however, can be created in the form by itself (or better yet a helper) with one hand the balloon opening pressed firmly to the filler neck so that the helium during injection can not escape once again escape on the sides.
Overall, we were very impressed. The handling is very easy and absolutely safe even for untrained and inexperienced. We had been no personal experience with the filling of helium and made it at the first attempt with this article.