There are limitation to the DNA test that make the process questionable.

You can really only relate to living people so you still have to go back to whatever reliability you put on the "historical" data.

The margin for error is pretty high.

The principal clues go all the way back to the dawn of time and don't tell you too much about the recent past.

Have a look at the Wikipedia article before you spend too much. Google some other critiques as well and then make your decision from an informed perspective.