Thanks for the great comment. I agree that you need to learn the grammar of a language. I personally have a pretty hard time internalizing grammar rules. Our head curriculum designer always makes fun of me because I want to ban tables of things (conjugations, etc) from the world. I can study and memorize it and then when I go to use it, totally miss and it's frustrating. But if I hear a sentence structure 30 times in a few weeks, I will often naturally start using it.
We try in our system to teach grammar through the same spaced repetition system - presenting a rule and then giving you a cloze test and spacing it the same as vocab. So we can know, for example, that your second person plural conjugation is weak and often missed, but your first person singular is strong because you always nail it. Then we can try to show you exercises that make you practice the weaker thing when you're in a live session, to reinforce it in a different environment and make sure you can produce it orally too.
Most recent research that I've seen, and the linguistics researchers that I've talked to, seem to conclude that there is little difference between being implicitly and explicitly taught grammar. That you don't need be explicitly explained the rule to use it consistently, but that the important thing is that your focus is brought to mistakes in form and you make an effort to improve those mistakes. There are a hundred studies on this and they all seem to come out slightly differently and generally not very significantly. That said, learners often like to know the rules, even if it's not significantly helpful for long term retention and production.
I would caution against recommending that people pick up a grammar book unless it's an incredibly good one. Most are dry and difficult and assume you know the vocabulary of linguistics, which most people don't. As we said, language is a marathon and it's hard to stick with if you're immediately and mind-numbingly bored, which grammar books are good at. I personally prefer to get communicative and work on fixing my grammar as I go, since it gives me momentum.
I like the middle ground that Chatterbug has taken. The grammar testing is interactive and you can reinforce good patterns when talking with human beings in a spaced way. I know my grammar is in many cases wrong when speaking in German, but most people don't seem to find the mistakes I make at my level particularly problematic, and it gives me time and confidence to focus on the forms that I'm getting wrong.
What's really funny to me is that watching my own videos right after I do a lesson, I notice many of my own grammar errors, because I'm hearing them and have time to think about them, but I don't always have time to pull stuff properly when in the heat of trying to formulate and speak a sentence in real time. But I belive that helps me improve faster and stay motivated.