15the hover is the point
Throw one and it behaves like an ordinary glowstick until it meets something solid, then it lifts off and floats several tiles above where it landed. It shuffles itself sideways first to find the position that lights the most ground, and under a low ceiling it simply presses flat against the roof.
where to use it
Water. It stays bright when submerged, where a normal glowstick dims, and the hover keeps it off the seabed instead of half buried in sand. Diving the Ocean for chests, or clearing a flooded cave, a single throw lights the whole pocket. On dry land the edge over the cheap version is thin.
getting them
The Zoologist only stocks these once all three fairy types are recorded in your Bestiary, which means the pink, green and blue variants that wander the caverns. Fairies are easy to miss because they lead you to loot and then vanish, so it is worth taking a swing at one until the entries are filled.