My students have used Deltamath for over 10 years. A few years back the statistics class looked at data and found that students who completed at least 80% of their deltamath work (on time) rarely received less than a C overall in the class. On the other hand, students who didn't complete at least 40% of their deltamath assignments rarely scored higher than a D in the class.
Students leaving critical "reviews" of this program only serve to undermine the value of this site as a resource in evaluating educational technology programs. The moderators should do a better job weeding out these kinds of reviews.