Origin Gale makes for a suprisingly good warlock or paladin even?

[Moonbane]

In act 2, player Origin Gale can absorb Shadow Weave essence from any one of the Thorm's. Giving you an extra lvl 3 shadow spellslot. You may need to have read the Necromancy of Thay for Forbidden Knowledge.
https://imgur.com/a/0IDQ4yV

I tested it as a warlock, you can spend the shadow slot on any warlock spell, but it will always be cast at lvl 3. Additionally its still long rest to recharge. Also its permanent, doesnt go away on resting.

Definitely would be -quite- valuable for classes with limited spellslots.