Longer blocks are useful when you are first building a difficult idea; switching becomes useful when you need to retrieve, compare, and choose between methods. Staying with one subject can reduce setup cost, but too much repetition of one question type can make performance look stronger than it really is.
A practical approach is to learn in focused blocks, then mix later. First stabilise the method, then interleave topics or subjects so the learner must recognise what kind of problem is present and retrieve the right approach without being told.
Use the Study & Learning Methods Hub for interleaving, retrieval, and revision design. For exam-shaped mixed practice, use the Examinations & Assessment Hub.