I would disagree with much of this article. While Duolingo in particular is popular, its main focus is on teaching translation. It's hip, but it's not about teaching how to speak and understand a language. Similarly, the focus on vocabulary study in the other tools has similar limitations.

Self study needs to be augmented or driven by spoken conversation practice in the least. Your brain is a neural network to learn language as audio input. While challenging, it's the most effective way. Google doesn't support this due to the link popularity of a lot of software-driven methods.

Disclaimer: My business in the online language learning space.