I don't understand the presentation. Allow the user to choose nationality from a drop down box, then show a world map colored various ways: - green no visa - blue for easy to obtain visas - red for difficult to obtain visas On a side note, it should probably be "United States citizen" and not "US". Also, US -> China is a very common route that requires a visiting / mailing your passport to a Chinese embassy to obtain…
Finding an actual authoritative source on Chinese visa requirements has been difficult - there's a lot of second hand information around, but nothing official that I can find.
I'll definitely use them again. The point though, is that for a nominal fee, it's just easier to have someone who does visas every day handle the China situation for you, at least in my experience.