This can be a useful tool, but let me explain something very important about genetics that these testing services don't advertise. Epigenetics.
Our DNA is passed on from our parents. Tall or short, eye hair and skin color, but what about health problems? Its not as simple as it seems.
You are stuck with your genes, but you can control genetic expression. To summarize biology 101, your DNA replicates due to enzymes and proteins. These enzymes and proteins can only function at a certain pH and temperature. So even if you have a cancer gene, it can not duplicate itself if the "environment" (a.k.a your body) is not one that is favorable for the proteins/enzymes to replicate.
So now we get the the million dollar question, what do I have to do to keep those negative traits from manifesting themselves? Its as simple as eat right, exercise, avoid toxins ( drugs, alcohol, etc...) and get adjusted! These things all promote an alkaline body environment that actually controls genetic expression. Now there are some genetic conditions that can not be overridden by epigenetics, however those are the minority and generally manifested at birth.
A hundred years from now they might actually be able to genetically make people Irish for a day and turn them right back just by manipulating genetic expression. Isn't the future a wonderfully scary place.