Hello all, I have created this homebrew magic item and wanted your opinion on the appropriate rarity, as well as its overall usefulness. Could you please share your thoughts?

Breastplate of Fickle Resistance (Requires Attunement)

This armor is a +1 breastplate, and allows the attuned wearer to roll a d6 at the end of
each long rest if they desire. Until this ability is used again at the end of a future long rest,
the wearer gains the following benefit based on the results of the d6 rolled:

1-2: Resistance to non-magical bludgeoning damage.
3-4: Resistance to non-magical piercing damage.
5-6: Resistance to non-magical slashing damage.

I have two thoughts here:

1. If the point is to make the thing unpredictable, it might be better to delete the part about rolling the die "if they desire". Otherwise, what may happen is that the user will keep rolling it day after day until they get the one that they think is most useful and then never roll it again, in which case it's not "fickle" anymore.
2. The 2024 rules don't generally make a distinction between "magical" and "non-magical" versions of a particular damage type anymore, partly because in some cases it can be hard to determine whether some damage types are magical or not. If you're aiming for this to be used by people running the latest rules, it might be better to just remove the word "non-magical".

As for rarity, this combines an element of an existing Rare armor (Armor, +1) with something similar to an element of a different existing Rare armor (Armor of Resistance) so I think it definitely needs to be at least Rare, and probably Very Rare.