At least, I think it's the smallest. It's the little sibling of the BurgerDisk and like it, it's daisy-chainable, which means you don't have to choose between a hard drive or your floppy drives.
Here's a short video of installing and booting from the DominoDisk: https://www.youtube.com/watch?v=vfh9eRBlvNY
It's available at https://www.colino.net/wordpress/shop/apple-ii/dominodisk/
Definately a cool little device. Good luck with your sales.