It works fast. If you serious you'll waste so much time trying to learn it through grammar books and internet vocabulary guides.I'll still use my sources but I'll definitely check this out.
This guy learned it pretty fast too here's his 18 month update
You must basically learn the kanas/kanji with remembering the kanji and then immerse immerse immerse as as possible daily and use srs to learn i + 1 sentence cards where u learn one word or specific grammar usage. For example I'll make up one (from the top)
この橋は長いね。
If you knew all the words except 橋 you'd make a card with the sentence on the front and on the back the definition for the words you don't know in English. You do like thousands of these and then eventually you start putting Japanese definitions on the back instead of English.