I personally find the ethnicity aspect of DNA testing to be amusing and of extremely limited utility. But in the context of a major family tree program, the results concerning your shared genetic data is supported by matches between family trees (or not depending on the accuracy of your own research). For example, here is a screenshot of my relationships on MyHeritage.com that is completely ignored by the above article and all of the other online reports.
The utility of this information from DNA testing is in direct proportion to the accuracy of your own research as supplemented by the record hints and other tools available on the website. In this case, MyHeritage.com is NOT junk science. The relationship matches are independently valuable regardless of the accuracy of the "ethnicity estimates." In fact, with MyHeritage.com, I can go much further and see the chromosome matches using the MyHeritage Chromosome Browser between me and up to seven other potential relatives at the same time. Since it is apparent that those taking the tests and then broadcasting the results have no real interest in genealogical research, the "junk science" issue is itself junk reporting.
On a practical level, the key issue is whether or not the person taking a genealogical DNA test is involved in serious genealogical inquiry. Many of the people whose DNA tests are reported on the genealogy programs as matches lack family trees that enable me to determine how I am related to a 2nd, 3rd, or 4th cousin. Taking a DNA test, as was done by the twins in the story, without doing serious research is nothing more than entertainment.
What about the differences between the various companies? So what? I have two different tests from MyHeritage.com and from Ancestry.com. In both cases, the relationships shown are accurate but vary because different people took the two different tests but both tests accurately identify close family members and other relatives. In my case, unlike many others, I happen to be completely aware of the identity of all of my close family members but this is not the case with everyone.
In short, as a genealogist, taking a DNA test is simply one more tool in verifying the accuracy of my own research. The fact that ethnicity estimates vary between genealogy companies is no surprise since I fail to see a consistent definition of ethnicity in any event.