Originally Posted by
Psyren
I'd say it's not exactly new, it's also known as bag of rats or boil an anthill or sacrificial lamb/sheep. Basically, any game mechanic that triggers on death, the designers should test what happens if you use that mechanic on a critter or insect (and/or multitudes). If the players get power or utility out of doing so, then the mechanic needs to be revised because they absolutely will try that in game. Unfortunately that wasn't the case here.
It's not that it's "overpowered" - but clearly if they meant for Hex to be undetectable they wouldn't have given it a verbal component in the first place. Compare Hex to something like, say, the Friends cantrip, which is much more clearly intended to be subtly usable mid-conversation and not noticed when cast (though afterward is a different matter.)