To me it doesn't worth, first because others Charm have more value in hunts, with more damage, more defense, more survivance and exp on a second point, the are only few creatures like Demons and Vampires to use this charm and get some profit, on third point you need lost some time to use the Obsidian Knife so it can decrease the exp/loot per hour too, to the end the price of 1500 charm points is too high by the value.