First of all, apologize for any English grammatical error in my question. Now I began to use LingQ for my Spanish learning, my third foreign language. I found that without a knowledge basis of plural/singular and feminine/masculine forms of words, it would be pretty hard for a foreigner, especially from a different language system, like me, a Chinese to set out from zero. Then I double-check the instruction of Japanese I am studying as well in LingQ. The way of LingQ handling the ending inflection of verbs in Japanese confused me even more that LIngQ simply put those different inflections into categories of independent words. For instance, -nasai(なさい)represents "one word" meaning the request of the object action. I don't know if this is a proper way of teaching.
Personally, I think LingQ is an ideal choice for teaching those languages with fairly simple grammar rules, like English and Mandarin, etc. When it comes to those languages with complicated or even awkward(nothing offensive, just grumbling) grammatical rules, do we need a grammar book to come with?
Nevertheless, I still believe the way LingQ has is one of the most work-efficient system to date.