buttons are very hard and hurt when sitting and playing.

A couple of things to consider: 1) the buttons on the top get pretty uncomfortable on your backside, 2) the space between the seat and the frame is just small enough, and the top flexes just enough that could really pinch your fingers bad if you aren't careful.

Now for some review saw that buttons were loose, on mine they were tight which was great,

I do find the buttons to be a tad harsh if I sit on them the wrong way, so that part could use some improvement.

More importantly, the buttons on the cushion are a little hard on the butt after a while.

when my kids play piano, the buttons bother them.

Decent quality, the buttons can become uncomfortable and cause you to shift your bum over to the more padded parts