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.
Way smoother than trying to convince the embassy in LA to process your application, and likely more convenient that going to LA in person (which might not even get you anywhere depending on the whims of the Chinese at that moment).
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.