I managed to persuade my 90+ aunt, last of her generation, to do a test with LivingDNA. I chose them because they seemed to have good reviews. The test was easy enough to do, just a mouth swab and post it back. I'm not sure that the reports told us much, basically that geographically her ancestors hadn't moved much. We didn't get any links to anyone with similar DNA. I got the impression that the service was being developed with new features to come. Presumably the detailed analysis will at some point be able to be used by other services and we have at least captured her DNA for posterity.
A word of caution. Someone apparently related to a second-cousin of mine got in touch with me via information on my family tree website so I put him in touch with my cousin and over the years they exchanged a lot of information. Eventually he produced a book, at some expense, detailing his family tree, sending over from the USA several copies (expensive postage!). He then decided to take a DNA test. Oh dear! Turned out that his mum had met the proverbial milkman and that all of his siblings were really half-siblings and that he wasn't descended from anyone in his expensive book.