I'm happy to help you out!
Since you mentioned vocab and grammar, let me tell you how those two are impacted the most!
Vocabulary:
1. Audio quizzing - practice listening to the vocab - this is 100% renshuu pro, and is not available to free users.
2. Sentence quizzing - I wouldn't say this is more efficient, but it is better. Sentence quizzing helps because you get access to thousands of sentences (and I am actually adding N5 sentences every day at the moment, so more and more N5-level sentences are becoming available). How do these help? Japanese is a hard language to think of in terms of English, so it's best to not only know the meaning of a word, but to see it in various situations (sentences) to get a better feel for how it is used. Sentence quizzing will help a ton with that.
Grammar
1. Content level - there are no grammar expressions that are locked behind renshuu pro. However, the number of sentences you get per expression jumps..I believe it's 3-4x when you go to pro. This ties into #2 above. Grammar is more complex than vocab, so it often takes seeing an expression in multiple different styles, situations, and tenses in order to really grasp it. The free content will give you a bit of comprehension, no doubt. But unlocking all those extra sentences will really help in deepening your understanding of the grammar.
2. JLPT style questions - these are pretty new. Sentence Jumble and Star Selection were designed specifically with the JLPT in mind, and so you can get practice with JLPT style questions right here.
Now, you did not mention Sentences, but this is an area that has a ton of content for Beginner <--> N5 learners (and we plan to expand out to higher levels). These focus on entire sentences (instead of a specific word or grammar element in a sentence), and have listening practice as well as the JLPT styles mentioned above.
Now, you said you are new, but you appear to be using an older account. New accounts get a chance to test out renshuu pro, so I went ahead and added that to your account as well. Check out the pro area of your dashboard, and you should have a 10 day free pass waiting :)
