There are many test kits on the market that claim that when you send in a sample of your DNA, they can return answers about potential health risks and challenges you may face. You can also find out more about your heritage from these products. But how many of these claims are true, and what is part of an overblown sales pitch? You can learn a little more about that from this video from Time.
If you send in a bit of spit, your entire genome probably won't be sequenced; companies use genetic markers to perform their testing, and the markers that companies use are not the same. So there may be some slight variations in the results you get back if you were to select several different kits, but it is likely that they are more or less reliable as far as ancestry goes.
As for health conditions, it depends on the disorder. We know a lot about the genetic basis of some, and very little about others. Also, some of the diseases you might be at risk for do not necessarily have treatments. And of course, being at risk does not mean you will get a disease. It's also important to consider the impact of your environment. As such, if you embark on genetic testing, keep the limitations in mind, and speak to a doctor if you have questions.