Is this custom Warlock Invocation for Pact of Chain balanced with published Invocations? [closed]

Question

The following custom Invocation wants to be used in my current game. Is this within the power range of published invocations in the PHB, or is it either too weak or too strong in comparison?

If this custom invocation isn't within the range of other invocations, how do I need adjust it to make it fit?

Eldritch Mutation

Prerequisite: Pact of Chain:

You can use a Warlock spell slot to cast a spell that will transform your familiar into a creature of higher power.

The creature it turns into must be of the same Race/Type as the Familiar, but with a Challenge Rating that is equal to half your Warlock level, rounded up.

While the Familiar is transformed it has its own initiative and it acts on its own. It's friendly towards you and your allies. However it does follow your commands (command takes bonus action).

The transformations last an hour and requires concentration. As a bonus action, you can end the spell early.

If concentration ends the familiar will go hostile towards everything on sight.

The familiar will go back to normal if its hit points hit 0 or after an hour has passed, even if you lost concentration.

Answer 1

Consider the following spells that are very close to what this invocation does:

• Conjure Elemental (5th level) allows one to summon a CR 5 elemental (available to any warlock, 1/long rest, at lvl 9, from the Minions of Chaos Invocation)
• Conjure Fey (6th level) allows one to summon a CR 6 beast or fey (warlock spell, available at lvl 11 with Mystic Arcanum)

Mechanics that are the same:

• Concentration, under control up to 1 hour
• Becomes hostile if you lose concentration, still reverts/disappears only after 1 hour
• Creature CR equal to slot level (up to warlock lvl 10)

Mechanics that can be easily adjusted:

• Casting beyond warlock lvl 11: This invocation continues to use a lvl 5 slot beyond warlock lvl 11 to create a higher CR creature. Since the warlock gets access to Mystic Arcanum for higher level spells, you should probably cap the CR at 5 for normal slots and possibly allow expending uses of Mystic Arcanum for higher CR transformations.

• Frequency of using this invocation: this Invocation seems to be usable at will whereas other invocations that allow casting high level spells usually allow only one use per long rest.

• Direct commands: this invocation is requiring a bonus action for direct commands while the spells require no action to do so.

• Casting time: the casting time for both spells is 1 minute

Final Comparison

Advantages of this invocation:

• Added versatility, allowing casting at many different levels to gain access to different CR creatures
• Control a different type of creature: warlock familiars can be fiends, for example, where the other spells are limited to beast/elemental/fey

Disadvantages of this invocation:

• The warlock loses access to his familiar while this effect is active whereas any of the conjure spells allow both a familiar and another creature simultaneously.
• This invocation is exclusive to pact of the chain warlocks.

Note that any proposed adjustment that isn't made equal should be appropriately added to the list of advantages/disadvantages.