Since 80% of Colonial US ancestry was from the British Isles, it may be possible to review the census, 1790--1940 now all on-line at a few libraries, the Census Bureau, and Ancestry.com in ancestral searches.
I think the testing may be valuable in researching family diseases, but am not convinced a firm connection to an 18th cousin can be established except at the 0.0165% level. I can see its use in paternity testing in legal cases as well as those who might claim to be a descendant of a famous person in order to claim a share of their estate or fame. Since I believe it is well-known that I am descended from Butler-Parker lines in the British Isles, I do not plan on an extra expense as so few are getting DNA tests & family lines vary from company to company. If somewhere along the line, a Parker married a Romanian gypsy & I can't prove it, it doesn't bother me.
Afro-Americans comprised 40% of the first immigrants, intended as slaves in Colonial America. Their Afro names may have been lost; women & children were not included in a census as far as I know at that time.