Quick add to cart by model or sku -help

hi,

Interested in Quick add to cart by model or sku extension.but just to need something before I purchase.

1) I have set up lots of products and these products have variations....eg size/colour.

Am I right to say the sku/model can only be set to the parent product but not the variation product.

So If a customer wanted a particular colour than this would not work??

Thanks