You mentioning that you don't have enough melta is an argument enough for the magma cutters rather than lasher tendrils, to me. Lasher tendrils don't keep the fellows with meltabombs and krak grenades from ruining your day, or reduce the amount of shooting coming your way.
What sphinx of plascrete and adamantium bashed open their skulls and ate up their brains and imagination? Imperator! Imperator!