The Hound is a improved Heightened Spell that isn't a metamagic, you can apply metamagic once. It works all spells, damages the enemy, can knock prone him and apply disadvantage for every spell casted. You can also cast multiple hounds for still more damage.
So, the Shadow Sorcerer can cast Mind Sliver and Quicken a save or suck spells. All spells is with disadvantage + Hound's damage.
Bane is a concentration spell, the best save or suck spells are concentration spell and you can't cast two leveled spells per turn. Bane or Hypnotc Pattern/Fear but not both. Mind Sliver + Save or Suck spells stacks.
Metamagic + The Hound stacks.
A good stack is Careful Fear/Hypnotic Pattern + Hound's disadvantage.
Let's talk this through. Shadow sorcerer decides to take on a foe within 120'. They use the first round to (Bonus) Hound, and cast a spell with a metamagic applied. Then, on the second round, they can mind-sliver and then cast another spell quickened spell with a very high chance of success.
7th level Shadow Sorcerer with an 18 Charisma (spell DC - 8 + 3 + 4 = 15).
Round one: They use the bonus (3 spells points) and cast a save or suck spell (hold person, hypnotic pattern, whatever). If they fail, the combat is essentially over. If they succeed, then we go to round two.
Compare that to a sorcerer that cast that same spell heightened - They did not use up their bonus action and the enemy is in essentially the same position if they fail the save.
Round one point five: Hound gets to attack somewhere in here for 10 damage or 17 if they are held (but you'd end the hypnotic pattern effect if you attack). If the enemy made their save, they get to do something, perhaps eliminating the hound (40 to 50 damage required, or a spell effect that otherwise negates it).
Round two: Assuming your foe made that save, you get to mind sliver (potentially your foe gets disadvantage) and then quicken (2 spell points) a save or suck spell. If they failed the save against mind sliver, this is going to be at disadvantage with a -d4 to the roll. Highly likely they'll fail. Let's say they have a +4. They have about a 10% chance to make that roll! Unless, of course, the hound was destroyed, in which cse you're not getting advantage on either roll.
Compare that to the Heightened spell caster coming back and doing that save or suck spell - There is a roughly 20% chance of them making that roll. So one time in ten you'll get a different outcome.
Shadow sorcerer is solid, but it isn't earth shattering. If I were going to rank the power level of the sorcerer subclasses, it would not be my first pick. Aberrant Mind - gets that nod right now.