If it's the balls or pebbles, not my first choice. What you want is more surface texture - jagged edges - like the perlite or pumice would provide. The jagged or rough edges help to prevent compaction and provide good aeration. Alternatives would be something like Turface (a clay product), granite grit or clay-based kitty litter (not the scoopable kind).

Coir is fine and a common alternative to peat. Go light on any compost or worm castings. Both will continue to decompose and particle size will decline and therefore the material will collapse.

All this is assuming you are using the mix for container planting. If amending regular garden soil, use whatever you have - garden soil is much more forgiving :-)

Coir is coconut fiber. Coco powder is what you make hot chocolate with :-) Coir is often used in potting mixes, typically sold in a compressed brick that expands and is reconstituted with water.

Could you smash up the expanded clay pellets, like with a hammer or such? They are just not going to provide any benefit otherwise.

Coconut coir is in the fiber form. Coco powder (yes, that's how it's actually marketed) is what you get when you take coco coir and put it in an industrial strength food processor. It's a direct recplacement for peat, minus the PH imbalance.

Could I smash them up? Yes. Do I want to? Obviously, not...

You can of course do whatever you like. However, leaving the expanded clay in its pelletized form will NOT have the same benefit as the perlite or pumice in the 5-1-1 mix. So not a good replacement material.

Perhaps it is a regional thing but I have never seen "coco powder" referring to a coir product. It IS ground coir fiber that the compressed bricks are made of but it is not commonly sold loose as a powder. And I am in the industry with access to a wide range of horticultural product vendors - none of them sell just the 'coco powder'.

Probably won't crush up the pellets. So I'll probably stick to perlite or vermiculite, and maybe just do a different use for the expanded clay. Maybe I'll take up bonsai, or something. (no, I really won't)

On the coir powder. I guess I'm surprised you haven't heard of it. Just this weekend, I was at a local farm that utilizes a Vertigro type system, and I must have been looking at about 3 tons of the stuff - aside from what was in the planters. They use the coco powder (which is also available at my local hydro shop) with about 1/3 of the pot filled (at the bottom) with pine bark. It drains out the bottom of one stacked pot, into the top of the next one, until it reaches the bottom. I'll see if I can get you a brand name on the "coco powder".

Coir is probably a bit better than peat moss because it is something that can be replaced annually, but is the shipping of that material really sustainable? Pine bark fines might be an even better material, depending on how far it must be shipped.
Both perlite and vermiculite are heated to cause them to expand just as those clay particles were. I don't find much about using expanded clay as a substitute for perlite or vermiculite, however. That may mean no one has done that or they do not want to report what happened.

I'm not looking at this too much from a sustainability point of view. I don't use much material, and I use "no till" organic methods to maximize the life and usefulness of my mixes. Since I'm not a commercial grower, I tend to grow my plants continuously, rather than establishing new stock every season. I'm going to do some experimenting with different variations this season. I wanted to hear some real life experiences with the expanded clay, but I'll still do some controlled experiments to determine usefulness. I appreciate the input so far. Please note, I won't be using experimental mixes for anything that matters. It's just for fun and learning, at this point.

How did the Leca go in the soil mix?? I'm trying it in a few of my plant babies, potted.

Do i soak they clay balls before i crush them? or can i crush them and not soak them ... 🤷🏽‍♀️

I've not used the clay balls in this way (in containers) but have used them otherwise. I find they have a tendency to crush to clay dust if 'crushed' - but if you want to whack them in a bag with a baseball bat you may get closer to what you want. If you can experiment, I'd try two pots, one with partially crushed and another just leave them as is. May depend on how pristine what you have is - when I've bought, a certain amount had some breakdown just due to handling. YMMV.

How did the clay balls work?