It's free!
And the additional spell (with a free cast) might be meh for a wizard, but for sorcerers, warlocks, EKs and the like it's pretty good.
Wither and Bloom and Tasha's Mind Whip* look like the strongest choices for black robes.
It is not free to use, you need to spend hit dice on it, so it is extremely limited how much extra damage you pass out over the course of a day, especially on a Wizard or Sorc with small hit dice.
Of course the feat is free, maybe that is what you meant?
The spell is nice, but other feats that give you a 2nd level spell also give a 1st level spell and a half ASI. There is no half ASI.
I actually think the feat itself and the free spell are best for clerics. It lets them dip into the Wizard spell table and their d8 hit dice are going to outpower the Wizards and Sorcerers. I think it is going to work well on my Paladin too and he is going to need the free cast to have
Strixhaven won't be permitted at the table I am playing on so it will be Tasha's Mind Whip.
For my Paladin I am going to get Hex and Dissonant Whispers at 1st level, pick up mind whip at 4th along with Cause Fear from Shadow Touched and boosting Charisma to 18.
I will have Dissonant Whispers, Mind Whip and the aforementioned smites to use it with LC (if my DM allows it).
One thing about the feat is it appears to be limited by the spell level, not the slot level so upcasting something like DW would not let you use 2 or more hit dice. This makes it a little tougher to use for multiclass characters I think.