I think some kinds need at least half a potato to grow, but it's good you have the kind that will grow from a small piece.

Trevor, where on earth (if it is earth) do you live that you can grow sweet potatoes this time of year?
I love sweet potatoes, baked then ozzing creamy butter...yum. Or mashed with pineapple bits,crushed pecans and melted marshmallows...heaven, don't you think?
How about slices baked with peaches and brown sugar and ginger? Or add cranberries for a tart sweet flavor.

How did you start those sweet potato slips?

I'e been growing some of the purple-leaved ornmental sweet potatoes and am delighted to see lovely purple flowers on them. the flowers are one inch trumpets, looking like a small petunia. So nice!

I found some info from University of Illinoise Extension about growing sweet potatoes.

GW Thread on making slips.

Here is a link that might be useful: Watch your garden grow: Sweet Potatoes.