Not good !
I was given many brushes from Sigma about 2 years ago, I really hope they improved their brushes since then.
The stippling brush is the worse. (and I had 2 of them). It looses hair, it's not full enough and the worst is the dye coming out of it when cleaning it.
The foundation brush is very harsh on the skin, same for the concealer brush.
The powder brush looses hair all the time, the dye also comes out of it.
The blush brush is ok, it's quite soft but it's density is not very full. I like to use it to apply bronzer.
That kit is not worth your money. The only brush I use is the blush brush which you can buy alone.