It is extremely useful. Thank you.
Yes it talks about spanish, which is a completely different learning experience. But the point is clear.
Duolingo can(!) help you learning a language. But Duolingo alone will not help you to master a language. But that was clear from the beginning.
I guess the general consensus that Duolingo might be useless is because people think/believe it's a 100% solution. But that was never my idea of Duolingo. It was more like a kickstarter to get into a learning habit.