You have to pick 1 instrument, and that's it. This kinda stinks.
You start with one instrument in your inventory but again, you can play any instruments that you find

Why would I waste an ASI/Feat on being able to play an instrument when it has no gameplay value whatsoever?
It can be used as a distraction (and to gain some coins if well performed) but I understand the sentiment of wanting more.
And I really think it's dumb to gain proficiency because you help Alfira write a song. Years of practice to gain a proficiency cannot be gained in a single session of helping a bard write a song. That's silly to me.
It's a little weird, but at least player have a chance to gain musical proficiency without a feat or being a bard x)
When you are proficient and fail the performance check you still play alright.
👍