Limitless is useful for English practice if you can already follow natural conversations. The language mixes everyday English with a few expressions that need attention, so it works best for learners who already have a solid base. At an intermediate level, the main story should be easy enough to follow. At an average of around 86 words per minute, the dialogue is generally manageable, though some exchanges require more attention. For learners around B2/C1, this can be a practical choice for building vocabulary range.
