I used to work in a warehouse, and we used these little carts called a Taylor-Dunn.
Here's one:
We used them for hauling orders, and pulling little 4x8 foot trailers for larger orders. Anyway, ours were governed to 7.5 mph, top speed. I was on one whose brakes decided to go away, and I stepped off the thing into a low riding shelf, at 7.5 mph.
Wasn't a disaster, but, it wasn't the most fun I ever had.
Pass on the 12 mph skates.