I just asked my son - if his typing were better, I'd ask him to reply smile. I'm meshing his and my comments together:

He says HeyMath is a lot easier than the Math Olympiad books. That's true because Olympiad-style math always carries a puzzle-like twist that he likes. The syllabus is a parallel of Singapore Math, but the questions are also simpler than some of the Singapore Math-style books I've seen. What's great is that the explanations are very clear and precise, which is a bonus when there's no teacher at the side. My son says they do have very cool games as well (his seating partner must be green with envy!)

The programme doesn't track progress like Aleks, so I'm glad he has a teacher/ teacher's aide to keep tab of what he has to do next. He definitely prefers HeyMath to Aleks because it has a much livelier presentation (not cutesie but very similar to the default Singapore curriculum, My Pals Are Here). They do have quizzes and the results (although I'm not 100% sure about this part) can be accessed by the teacher.