Bump stocks are worthless. Objectively. They reduce accuracy and can only spray randomized rounds down range. You can just add easily provide suppressive fire in semiauto.
They might be fun, but they waste expensive ammo.

An argument can be made for somewhat improved accuracy with a pistol brace if you practice while wearing it. And you take the time to quickly strap it on when you need it.

And it's a hindrance is a round gets jammed and you have to clear and reload while it's strapped on if you haven't practiced that drill while it's strapped.

They mostly look nice.