Battery-operated guns definitely won't be powerful enough to flock a pony with. They're about on par with the hand-operated ones that rely on static to make the flocking stand up, honestly. Professional flocking systems use very high voltages because they have to, there's really no safer low voltage alternative.
A lot of flocking guns like that ebay one are designed for flocking wargame scenery with grass flocking... which is intended to end up scraggly and not entirely straight. The guns will work for those purposes, but not for a solid, even, soft coat like you'd want for restoring a SoSoft.