This site reviews courses, and NotebookLM is not a course, so a word on why it is here. Over the past couple of years the question I get asked most often is not which course to take but how to actually get through the one somebody has already started. People stall halfway through a textbook, cannot follow a paper, lose the thread of a lecture series. NotebookLM is the first tool I have used that meaningfully helps with that specific problem, and it deserves a place alongside the courses it supports.
The core idea is grounding. You upload sources, PDFs, documents, links, slides, transcripts, and the model answers from those sources rather than from its training data, with citations pointing back to the passage it used. That constraint changes the experience completely. A general chatbot asked about a concept will produce something plausible drawn from everywhere, and you have no way to check it against what your course actually taught.
NotebookLM asked the same question answers from the chapter in front of you, tells you where it got that, and lets you click through to verify. For studying, that difference is the entire ballgame. Where it earns its keep is interrogation. Upload the three papers you have to read this week and ask what they disagree about.
Upload a textbook chapter you have bounced off twice and ask it to explain the derivation on page forty in different terms. Upload your lecture transcripts and ask what the assessment is likely to test. This is not the model doing the work for you, it is the model acting as a patient tutor who has read exactly the material you have read and nothing else. I have used it against dense machine learning texts and it consistently unstuck me faster than searching for someone else's explanation online.
The Audio Overviews get the attention and they are genuinely clever, generating a two host discussion of your material that is engaging enough to listen to on a commute. I have mixed feelings. They are excellent for a first pass at unfamiliar material, giving you a shape to hang detail on later, and excellent for revisiting something you already know. They are dangerous as a substitute for reading, because they are pitched to be pleasant and they smooth over exactly the difficult parts where the learning lives.
If you find yourself listening to an overview instead of working through the chapter, you have made the tool worse than useless. Google has been generous with the free tier in a way that is genuinely unusual. Every core capability, including the audio and video overviews and the research features, is available without paying, and the paid tiers raise limits rather than unlocking functions. The caps on the free tier are on sources per notebook, notebooks, daily queries and generations, and if you are working across a serious reading list you will hit the source ceiling before anything else.
Whether that is worth upgrading for depends entirely on how much you are studying, and I would use the free tier for a month before deciding. Now the honest limitations. It still gets things wrong. Grounding reduces hallucination substantially, it does not eliminate it, and the failure modes I see most are with mathematical notation, dense tables and anything where the meaning depends on precise structure rather than prose.
It will confidently misread an equation. The citations make this catchable, which is the point, but only if you actually check them, and the smoother the output the less inclined anybody is to check. The deeper concern is pedagogical rather than technical. Learning hard material works because of the struggle, not despite it.
Sitting with a confusing passage until it resolves builds something that having it explained does not. A tool this good at explaining makes it very easy to never sit with anything, and to finish a course with a pleasant sense of comprehension and no retained capability. I do not think that is a reason to avoid it, but it is a reason to be deliberate. My own rule is to read first, get stuck properly, and only then ask.
And it will not tell you what to learn. It has no curriculum, no sequence, no assessment and no opinion about whether you are ready to move on. It is entirely reactive to what you feed it, which makes it a superb companion to a structured course and a poor substitute for one. My 4.0 is for a free tool that solves a real problem better than anything else available, marked down for the ease with which it can be used to feel like you are learning while doing nothing of the sort.
Pair it with an actual course, read your sources properly, use it when you are stuck rather than instead of getting stuck, and it will earn its place in your week.