So me and my DM are home-brewing stuff for his campaign, and I had an idea for an enchanter special ability. It's either highly niche or easily exploitable, but I honestly can't tell.

Cameraderie- When you cast an enchantment spell of 1st level or above that charms a creature, the target and you gain temporary hit points equal to your proficiency bonus. When the spell ends, if the target still has these temporary hit points, it doesn't know it's been charmed (although it's attitude to you reverts to normal).

Currently it's attached to a Druid Circle and a Witch Coven (homebrew class currently in play test) rather than Bard or anything more charm based. Thoughts?