Women must test male ancestry through a male relative. Results take about six weeks. For privacy, Family Tree DNA keeps test results in a computer not connected to the Internet. In the lab, clients are identified only by a number. Greenspan is candid about the limitations.
Testing is only another genealogical tool.
You're not going to know if someone is your great-grand uncle using this, but you will know if he's related. The only thing determinable with 100 percent certainty is an ancestor shared within the last 1,800 years. That's why some geneticists think DNA testing can't tell genealogists much at this stage. However, the resolution will continue to improve as more genetic markers are identified. For instance, Underhill points out that some non-Jewish men in the Middle East probably share the Cohanim Motif, so it's not unique.