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It's the same guy. I can't speak to the app, but the book is extremely good. I actually funded the app on kickstarter, but by the time it came out, I had already done the process from the book.
Some of his ideas that I was able to put into practice:
1) Learn sounds FIRST...too many people don't learn pronunciation and then can't fix it later. Book has a lot of concrete advice about how to go about it. (Probably contained in the app.)
2) First learn a list of around 600 concrete words, learn them by making flashcards with pictures. (He'll give you the list.) Use google images to search the words IN L2.
3) Then learn a frequency list. (Most frequent 4000 words or so)
4) When choosing immersion, go for TV series that you have seen before in L1...you already know the characters and what is going on and can concentrate on the language.
There's a bunch of other hacks...how to memorize gender and such. All very good and practical.
There's a robust language-learning community online of people who have worked on exactly this sort of challenge. Fluent Forever is a great guide to independent language study. Lingvist and lingq are both examples of well-designed online systems that can help provide a framework for things, though I haven't used them extensively so YMMV. If you're looking for a challenge or a community, the Add1Challenge is an intense group that provides resources and support to reach the point of having a 15-minute conversation in your first three months of study. Lastly, italki lets you find partners to practice language with: it can pair you with a French speaker trying to learn English, giving you each equivalent language practice time.
In general, vocab is king in language study. You'll probably want to find a good spaced-repetition system, which is a well-regarded method for actually consistently remembering what you are studying, whether it's vocab or anything else. Anki is a popular one that I have used and enjoy. If you want to get far in the language, I'd actually recommend against Duolingo except perhaps as a motivational/relaxation tool--it's not going to get you further than the very basics of the language, and can give you the illusion of making more progress than you are.
While there are a ton of resources, the really important thing is to start doing something, and learn what works as you go along. Languages are huge, and satisfying to study; by far the most important factor in succeeding is how much time you're willing to put into it.
If you've got any other specific questions about language learning I'm happy to talk about it all a bit more--it's a satisfying hobby and there's a lot that can be done.
I'm going to give you some advice that I hope you take to heart. Your study process, meaning what you do with the material, is far more important than having "the best resource".
If all you are doing is using a resource, you will not learn the language very well at all. You have to cultivate a better process to work with the resources you have.
You have to learn actively. Guess at the meanings of words before you look them up as this will help the meaning stick. This is why people feel that learning a word in context helps them remember it better. It's not a magic component of context that helps, it's the the act of struggling with the meaning before the meaning is made clear.
Use and review the material that you learn in an iterative way. Integrate material you have already learned into the process of learning new material. If you learned vocabulary for family members last week and you are learning the past tense, write about your family when you were growing up. If the next week, you are learning about dates and times write a few paragraphs talking about your family from 1800 to the present (even if it's fiction). This creates a web of concepts in your mind and is superior to learning things in isolated sets.
Seek feedback regularly. Ask native speakers to help you and evaluate your progress. Test yourself to get a reality check. You will convince yourself that you know the material you have covered because when you review the book it seems familiar. This is a lie. The way you know that you know the material is by using it in unfamiliar situations. Use practice tests and fill-in-the blank exercises to check your progress. You must actually take the tests and do the exercises. If you don't actually go through the process of writing in the answers, you can trick yourself into thinking you know the answers better than you actually do.
This sort of learning is hard because you have to face the fact of your learning and not how you wish it to be. Too many people use their resources to the point where they can almost recite it from heart but then when faced with a native speaker, they can't produce. It's because they mistake familiarity with the text for mastery of the concepts. Take a look at the progress that u/shiner_man made in just 90 days. He made his own flashcards, worked through his material repeatedly and in different ways. That's how you leanr a language. Of course you don't want resources that are crap, but at a certain point the way you work is far more important than having "the best" course.
Read these books:
Fluent Forever, Gabriel Wyner
Make it Stick, Peter C. Brown