Not sure if this got said earlier, but with Aberrant Dragonmark, the HD effect is still worth it. It only damages you if you have no enemy within 30 ft, otherwise it damages an enemy, which obviously is good. And sometimes you don't have THP, for one reason or another. So if you have no THP (or very little) and you have an enemy within 30 ft when you need to Shield, it's definitely worth popping that hit die.