I uploaded my raw data from Ancestry (only one of the three companies with which I've tested) to DNA.LAND. I knew that many people had no matches and that most only had a couple. I was lucky. I had 5 relative matches. Most of those were persons with whom I'm already in contact. At least one is someone who may be hiding under another name but that I did not immediately recognize as a match at any of the companies with which I've tested. As the database grows, the number of matches should increase.
I like the way the match is represented on the chromosome browser from the match screen. I like that we have segment information that is predicted to be recent or ancient in a table which can be unhidden. Most early adopters also comment about liking this.
I found the Ancestry report, predicting my ethnic or regional origins, to be very similar to the original ones produced by Ancestry before they introduced an algorithm which broke the report into more specific areas. The admixture tends to be the least reliable part of a DNA report, yet it is why many people test. I'm still seeking the alleged Ashkenazi/Levantine (or Eastern European Jewish) ancestor.
How useful is it? Not very useful at the present.
Does it have the potential to be useful? That depends on what features they introduce. (Part of an answer to a question in the "Help" section states, "We will be adding other features to the website that you
don't get with other sites. This is just the
beginning. Early adopters will help us to validate our
approach and to continue our efforts.")