Pact of The Chain Familiar and Magic Stone: can an Imp (or another Familiar with Arms / Hands) Throw the rocks?

Question

I gave a pouch, filled with some pebbles, to the Imp to hold.
On my turn, I cast Magic stone with my bonus action and attack with some other cantrip like Mind Sliver or something.
Then on the subsequent turns, I use my bonus action to make the Familiar attack with his reaction by throwing the Magic Stone, and then at the familiar turn, it uses its action to throw another stone.
Now level 4 I'm making 2 attacks with magic Stone, and if I need I can use my action to debuff with a cantrip or something like that.
For more context, if it is needed, I also have the invocation "Investment of the Chain".

I noticed that because of how Magic Stone works just like a weapon attack, I kinda ended up getting the equivalent of "Extra Attack" before the melee characters of the group, so far it didn't really upset anybody or anything I was just wondering if this is a legit use of those spells and features, or if I'm misinterpreting how things should work.

Overall I see this as some earlier "peak" of power before level 5, but I assume that after that this strat will be inferior to the actual "Extra Attack" since the Magic Stone spell only produces 3 stones per casting, so after you throw all of them you have to lose one of those attacks to refill, and also it's limited by how many stones you have. But I'm curious if I just found a fun interaction in the game that I don't see around, or if I just never saw that around because it isn't possible.

I saw that there is a similar question to this one in here But as you can see, the "accepted" answer only talks about the normal "Find Familiar" Spell rules, and don't really mention how the Pact of the chain interacts with it.
The other answer that got downvoted does try to make the point in favor to Pact of the Chain familiars being able to use the stones to attack, but it makes some weird points about "rules of permission and forgiveness" that I never heard anything about in the D&D Community.
I also don't see any comments on their answer negating their points, only the -3 votes are a point against their logic. So I want clarification for this situation in specific.

Answer 1

There are no rules preventing Pact of the Chain familiars from using their hands

Normally, familiars are limited to animal forms and cannot attack. The Pact of the Chain unlocks new, more powerful forms, which have hands and can attack with their Reaction in lieu of one of the PC's Attacks. If the PC also has Investment of the Chain Master, they may (as a Bonus Action) command the familiar to take an Attack Action. In other words, this is not the mechanical equivalent of an Extra Attack that some classes get at 5th level because you must spend your PC's action economy in order to buy the familiar's ability to attack.

So, yes, Pact of the Chain familiars can make attacks with the "magically imbued pebbles" produced by Magic Stone, but not exactly as you described it.

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In your case, the imp can immediately make an attack with its Reaction, if your PC takes the Attack Action and forgoes an attack. Furthermore, your PC may, as a Bonus Action, command the imp familiar to take the Attack Action on its turn (thanks to Investment of the Chain Master). In both of these cases, the familiar may

make a ranged spell attack with one of the pebbles by throwing it or hurling it with a sling.

Notably, the range of this particular ranged spell attack is 60 feet, if thrown, and 120 feet, if slung. So, you can think of the range as 60/120, if the familiar has a sling. And, if the familiar is within 100 feet of the PC, the familiar can deliver Magic Stone as if it had cast it.

Finally, even though the familiar can throw the pebbles, sometimes it will be more effective to pass them to an ally. The familiar may, e.g., deliver the spell with its Reaction, then on its turn, pass the stones to an ally with a Free Object Interaction and use its Action to do something else even more mischievous--like, Help, administer a potion, or turn invisible. This way, the damage per turn actually scales with those allies' Extra Attacks. Such a strategy is particularly effective when your allies might otherwise spend their turns don/doffing a shield to get at a bow, or find themselves perpetually 'dash[ing] towards the enemy!'.

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Extra hands are part of the appeal of Pact of the Chain familiars

A Sprite, e.g., indisputably uses its hands to wield its longsword and shortbow; it would be incongruous if a sprite familiar easily performs feats of fencing or archery but balks at tossing a rock (moreover, a magically empowered rock)! Hands enable these familiars to open doors and windows, pick locks, pilfer, signal, operate mechanisms, trace runes, or carry and/or throw items. They are truly invaluable for the creative player!