I would have to say the article is a waste of space, simply because what was written could be written in about 2 sentences, i.e:"Hold this 5note chord in both hands, now simply repeat each finger in each hand until you are exhausted. Trust me, this will make your playing good enough for Rachmaninov."make your own decision if this is good advice or not!
I skimmed the article and saw many things I think are basically good. Finger independence is really the root of all problems in piano playing, and ultimately the largest test of any artist.That being said (for the sake of brevity without justification), the idea of building finger muscle is a fallacy. Look at a video of any pianist who has been practicing all their lives; unless they were born with thick, muscular fingers, that doesn't generally change. The muscles develop in the hand.
Finger independence is really the root of all problems in piano playing, and ultimately the largest test of any artist.