The Angel Demon are a species with healing powers that can temporarily reject those powers for a huge strength boost.
Honestly? Mediocre. Their Shift merely turns them into a Succubus for 5 turns, which they can't even choose to cancel. During that period they lose their skillset as Angel Demons, but keep the stats as a support unit which does them no favors in performing in a seduction role. They're not the best healers either.
You may be interested in having them if you want to start with a sturdy healer as they have the second best durability of Lymean hybrids, and can DrainMana onSeduce which gives them more range than most for stealing Mana, but that's about it.
Their personality seems to shift by transforming. In their normal form they want to keep their body untouched, while in Succubus form, they just try to fuck everyone around them, to make up for their suppressed urges.