Maxed out Attributes/Crystals should have an indication
Coming from 1.12 Astral, Size maxing out at III is confusing, this is exacerbated by Purity and other attributes maxing out at II, so I suggest having a color change in the number when it reaches it's maximum value.
Same thing with Crystals, having a way of knowing when it can't fit any more attributes would make it more intuitive. Suggestion, have a tooltip (ie. This crystal seems to be too unstable to improve) or a color change on the crystal name.

Size and Tool Durability should be mutually exclusive:
I expect the size to affect the durability of a too made out of crystals, that's why I think that Tool Durability is redundant.

I created this comment on DW20's latest video of his 1.16.4 Let's Play, and though it would be helpful to elaborate on it here.

My opinion about the new Astral Crystal Mechanics:

tl;dr: Overall big improvement. Sad about the limited automation options

Good things about previous Astral Crystals:

1. Besides cutting, everything else was fully automatable
2. Stats were more straightforward & had clear maximums
3. You could repeatedly get perfect crystals

Bad things about previous Crystals:

1. The process of getting a perfect crystal was grindy and not fun unless you, like dire, had fun automating them
2. Even when fully automated, you still had to cut them by hand and grow them back up to full size.

Good things about new implementation:

1. You can't make a "perfect" crystal, you have to tailor make them for each purpose.
2. There is a clear way to make crystals with the stats that you want, but it isn't trivial to do.
3. The stats are small numbers.

Things that can be improved about the new implementation:

1. A maxed out attribute should have an indication of that (like the color change in old astral, ie. change the numerals from orange to green/red)
2. A crystal should indicate that its "full" (has all its slots filled), suggestion, change crystal name color.
   (Dire didn't read the astral book on camera so maybe its there, but)
3. It's difficult to know what each of the new attributes does.
4. I expect the Size attribute to impact tool durability, but there is a Tool durability attribute, and that makes size kinda redundant imo.