Requires lvl10 and no engineering skill. Also does a serious amount of damage for such an early explosive, while also not being too costly on materials, using only some copper, linen cloth and rough stones.
Unlike the goblin sapper charge, its bigger cousin, this has a 1 sec cast time, but only 1 min CD.
As for the damage.. I'd say it is very formidable. An avg of 150 damage is about the same as Iron Grenades, an explosive meant for lvl30-ish players, and at lvl10, you could round up a good amount of mobs and blow them all up with this. Mobs in that bracket only have like 250-500 hp each, so this explosive will carry your leveling.
Shammy and warrior tanks could also use this for snap threat in dungeons till SM, and then switch to Ez-Thro II if they like. Possibly add in an immolation oil for even more carnage.
My verdict: an underrated toy, especially for challenges.
Edit: just noticed my druid is unable to use this in bear form. So much for that idea...