So the final ability unlocked does not seem thematic, as it turns the spell book into a horcrux, rather than a method of manipulating magic. So I propose a couple of alternatives in the same line;

1) Choose two meta magic abilities when preparing spells following a long rest. You may apply each once when casting a spell during that day. You may apply both to the same spell. This refreshes when you take a long rest.

2) Choose two meta magic abilities to add to your spell book. When adding the meta magic to a spell, use an additional spell slot with a level equal to or greater than the number of sorcery points required to cast the spell. This may be done a number of times a day equal to your proficiency bonus. The meta magic abilities chosen may be exchanged if a week is spent meditating with your spell book.

D&D Beyond is run by a different company (Curse/Fandom) than the company that makes D&D (Wizards of the Coast). As such, your feedback for the UA class is probably going to fall on deaf ears, or at least the ears of those with no power to change the playtest material.

Unfortunately the survey for the Order of Scribes has closed, so you've likely missed your chance to provide feedback through the designated channel either.

Davedamon is right. Currently, the only thing WotC is accepting feedback on is the Feats UA. If giving feedback on UA articles is something you wish to do, follow this link, the surveys they post here are the only official way to give them your feedback. But we can only give feedback on the open surveys, and they only stay up for about a month.

https://dnd.wizards.com/articles/unearthed-arcana

Sigh. Oh well. Will likely run it as homebrew in campaigns I participate in. Thanks for the info.

If you have any opinions about the Feats UA, fill out the survey now before it closes. That link I gave you will lead you to within a click of the survey. I mean, you missed your chance on that subclass UA, but there’s no reason to miss the current one.