The claim is that the site has listed and counted all the names appearing in US Census reports and can tell you how many times your first and last names appear, and how many times they appear used by the same person.
It's much quicker, with a very "compact" report that may be of some help as a starting point for more specific searches.
It claims that there are 5,12,015 people in the US using my first name, and that it is the second most popular first name; that 99.63 percent of those using it are male, and lists the first five most common "variant forms" with an option to check the number using each of 11 variant forms.
There are 581,623 people in the U.S. using my last name, that it is the 27th most common last name, lists 5 famous people using it, and gives links to searches on 16 famous users.
There are 9,547 people in the U.S. using both my first and last name.
Results, unfortunately, are for US Census information only. (For those elsewhere it might only suggest how many of your clan had the good sense to come here, so you can puzzle over why they left you behind?)
Perhaps there are similar sites for other countries or perhaps other subsets of populations?