First Comment

This stone seems quite... underwhelming for a legendary. When I hear legendary, I expect something super fancy. A simple stat on a stick is boring! Not to mention it's destructible!

Yeah, a +5% is not to be underestimated but when you compare it to one of those books that gives you a +2 to a stat that are very rare (like the manual of quickness of action) it seems very lackluster.

Honestly, I think this is very good, effectively +1 to all proficient skills, saving throws, attacks, spell and ability saves. For rogues and bards especially.

I agree with Jupiter.  Perhaps not as good as some legendary items but it is legendary indeed when you consider how few options casters have to buff their spell DC and attack mod.

Deffo hefty on any character with the ability to get expertise.

a Tashas beastmaster rangers companion effectively gets: +1 ac, +1 all saves, +1 all abilities, +1 to attack and damage, while the beastmaster has this one active...

With more subclasses and races depending on proficiency to determine things like number of uses per long rest, multipliers, and boosts for non skill related calculations, proficiency is going to become more beneficial overall.

As a general rule a character can only advance their proficiency 4 times across 20 levels.  This item gives an across the board bump unlike anything else.

This stone has gotten really good with the new features that grant uses based on proficiency bonus!

It's a shame this would be instantly destroyed by pretty much any AOE damage effect a level 11+ player character would come across

Quote from polymeri >>

It's a shame this would be instantly destroyed by pretty much any AOE damage effect a level 11+ player character would come across

 It would be a dick DM to break something like this so easily.

Quote from polymeri >>

It's a shame this would be instantly destroyed by pretty much any AOE damage effect a level 11+ player character would come across

 From the text: "It is considered to be an object that is being worn while it orbits your head." While meteor swarm damages ALL objects in the area (another reason that spell is overpowered), I'm pretty sure this would protect it from most AoEs.

Edit: that said, it's still really fragile.

Why can’t I search this item? If I put in Mastery, or try to filter items by “Bonus, Proficiency Bonus” I get errors.

Agreed.  Prof bonus caps at +6. This is worth 16% of max prof bonus. And prof bonus averages to +1 every 3 levels. It's a great item. That said, I'd take it as minor, lesser and greater with +1, +2, and +3 bonuses.