These little hooks were manufactured out of metal straps that cost $0.92 instead of paying $50 to $80 for mass manufactured tools.
The concept is simple, slide the hook onto the top of the last plank installed and rest the next plank in the hooks that hang out. The new plank is now level, straight, and held in place while you are free to move around and screw it into the studs.
You don't have to measure and hold each plank as you try to get a uniform result, instead you simply rest the plank and get to work. It is a good idea to audit your work periodically and measure the amount of plank displayed to make sure you are within the tolerable limits of your job.
When you are shopping for tools for your project, don't be swayed to purchase the most expensive tool for the job and focus more on making the right tool for the right price for the job!