Simple

Can we talk about how busted it is to give a 4th-level character access to 6(!) Uses of a 5th(!) level spell. It has 40hp, 2 +9 attacks (Avenger has 600ft range!), Defender has 18AC (!)

This is a pretty average spell for a 7th-level character but for level 4!?!? This could turn the whole adventure into Angel Summoner and the BMX Bandit. Yes, it uses concentration, but it lasts an HOUR!

Then just don't give it to a level 4 character??? Simple as that???? The DMG recommends one very rare item in the party for levels 5-10. If you are giving 4th level characters Very Rare items then yeah the VERY RARE ITEMS are going to be unbalanced. Yeah, it's average for a 7th-level character, because Very Rare items are designed for use by level 11-15 parties.

Quote from Grayseeroly >>

Can we talk about how busted it is to give a 4th-level character access to 6(!) Uses of a 5th(!) level spell. It has 40hp, 2 +9 attacks (Avenger has 600ft range!), Defender has 18AC (!)

This is a pretty average spell for a 7th-level character but for level 4!?!? This could turn the whole adventure into Angel Summoner and the BMX Bandit. Yes, it uses concentration, but it lasts an HOUR!

The adventures (so far) that include the characters that have these items at 4th level are designed to introduce the new rules. After running one of these, I also believe they are trying to encourage GMs to bring the danger level up in their encounters. I ran " Uni and the Hunt for the Lost Horn" for my group and by the end "Niko" was dead, the item didn't help them much against a cone of cold. 

This item is fine, as you said, for higher level players but if you do put it in the hands of lower levels, make sure the challenge level ramps up with it. 

Gotta love that the mace that can summon a f*cking celestial spirit 6 times a day is presented alongside a bow that makes ladders...

Also the celestial spirit is large and can just fly while carrying people.

Also both items are presented as equipped by level 4 PCs, with the bow being given to a ranger. The celestial from this mace has a higher to hit bonus, deals more damage per hit (even if the ranger is using hunter's mark), and the celestial can attack twice where the level 4 ranger can only attack once.

Long story short: WOTC still really hates rangers.

NIKO ONESHOT IS THAT YOU????!?!?!?!?

Why does it say it's found in the DMG when it's not actually in the DMG?

Thi sjust needs to switch to 1/ per day or change the spell. But there's no way I'm letting lvl 4 pcs have this as is. 

Give this to the messiah.