Please, don't do it.
Disco Dust is not an edible product, and it is clearly labeled "For Decorative Use Only."
Disco Dust is a fine-grain plastic craft glitter. It is not food. It is not to be used on food. Simply because it is labeled "non-toxic" does not give you license to feed it to people. Crayons are non-toxic, yet (hopefully) no one serves crayon shavings on cupcakes. Sharpies are non-toxic, yet (hopefully) no one writes messages on cakes with Sharpies.
Disco Dust is meant to be used on decorative elements that are to be removed from the cake prior to serving, not fed to unsuspecting people who TRUST that you are feeding them 100% safe and edible ingredients.
And justifying that you use this because a) other people do it and b) you haven't sickened anyone yet is NOT acceptable.
There are edible alternatives out there. You can now buy 100% edible, FDA-approved pearlized Crystal Colors from www.sugarpaste.com. They are made and bottled here in the US.
Be professional. Be educated. Be ethical. Just say NO to feeding people Disco Dust! :)
The following is a letter from my local health department ordering cessation of the use of Disco Dust on food. Please read and share.
DISCO DUST.pdf 35k .pdf file