I've been using Math Academy for a couple of months now seriously (~3.5k XP). Initially I was reviewing topics / concepts that I already had an intuitive understanding of from college courses, and I believe for those it has helped take me to the next level in that I now can, 99% of the time, solve problems in those topics. As I start to approach topics that I haven't fully covered in college or have some intuitive understanding for I do find that I can mechanically carry out the operations, but I lack an understanding of "why" I'm doing this.

I think the author of this makes some good points to this effect. I believe that the best approach is a bit inverse of what the author is saying however. I think that Math Academy should be the base, where 80-90% of your time is spent. The remaining 10-20% should be used to supplement this. Either with lectures, textbook / edutainment reading or other ways to develop more of that intuition.