A gazillion balloons? I would have thought setting up a clinic for, or at least paying for the medications that some mito patients need that aren't paid for by NHS would have been entirely a better use of the money. Education efforts would also have been a great option. A respite opportunity for a family of someone (of any age) who has one of the really serious mito diseases. Research, even. While the balloons money wouldn't have bought much, it could have bought some time or resources for a lab where they're trying to sort out what's going on. A scholarship in the boy's name to a medical student who wants to research causes/treatments/cures.
Another "feel good" stunt for a group. But then, I've never really understood the formation of this type of flash-mob. I have to conclude that the little boy, while the focus of all the energy, was not the real motivation there.