30Used to craft
throw it, do not hold it
The treasure glow is centered on the stick rather than on you, so keeping one in your hand wastes most of its range. Toss it down a shaft or across a cavern and it lights up ore you have not walked to yet. Everyone on a server sees the shimmer, so one person can scout ahead for the group.
where it stops helping
Every buried thing gets the same yellow shimmer, gold and copper alike. Early on that is fine, because you want all of it. Later you are digging past hundreds of worthless veins hunting one specific ore, and the potion, which color codes what it finds, earns its brewing time. A Metal Detector helps a little, since it names something valuable in range, though not always the nearest thing glowing.
The Magic Lantern covers less ground but never leaves your side and never runs out, so once you have one the glowsticks become a tool for scouting past your own position rather than a light source you rely on.