This is a great product and it works very well with the grinder. Obviously this needs the grinder to work and is therefore more of a grinder attachment rather than a mixer attachment.
Sausage casings (skins) are easy to find online or, if you're lucky, your local butcher can give you some when you're buying the meat to stuff them.
However, whilst I expect to pay a little more for the KitchenAid brand and quality, this is a bit of a hard pill to swallow. Whilst the cost of [...] will be amortised over time in sausage savings it is simply two funnel shaped tubes made of fairly cheap feeling plastic. I suspect that the huge manual and box they come in cost more to produce than the "stuffers" themselves! That is the only negative point and the reason it has lost a star.