Instruments of the Bards seem way overpowered

[diplomancer]

An uncommon magic item (some of them) that gives access to 7 different spells (greatly helping with the spells known issue of the Bard class), once a day each and almost insures that Hypnotic Pattern will hit almost everyone.

I dont see any other uncommon, or even rare item, that is close to its power. It seems that the only balancing factor is that its limited to bards, but its not like bards are an underpowered class.

[darknite]

At higher levels the disadvantage vs charm effects can be very potent, depending who it's used upon.

[DMThac0]

They start off pretty powerful, assuming the players get their hands on one early. However, in my game where I customized one, it's become a "swiss army knife" in a sense. The player has access to many other tools and abilities so the instrument is just another cog in the wheel. Yea it's a great find, but it's not going to be that big of a deal in later game material.

[Karnitis]

As someone who's used it before, I purposely avoid breaking the game so I didn't use the instrument all the time. However, I do think it is somewhat OP because it is a Swiss Army Knife. With the instrument covering things like control spells (fog cloud) and utility (levitate, flight) among others, I basically can prep my exclusively offensive spells. Including the charm spells.

I wouldn't limit the weapon as long as the Bard doesn't have Main Character Syndrome, but it definitely gives the Bard potential wizard-like in utility while still retaining all the other goodies a Bard normally has.