Cakras (chakras), nāḍīs etc. are always imaginative (they never have been otherwise) and are ‘real’ only to an extent, just as a library cataloguing system is ‘real’ – therefore many similar/diverse systems can do the same thing (or less, or more). You cannot touch cakras, but muscles and organs (to some extent) yes, you cannot touch an abstract cataloguing system itself, but books yes.
Kuṇḍalinī is not a mystical concept, it is a philosophical concept dependent on the śākta-śaiva world of esoteric polarity. That’s why Buddhists have no (and need no) kuṇḍalinī, that’s why the Ṛṣis of the upaniṣads did not speak of it. Kuṇḍalinī is just a concept, a symbol. But this does not mean that what is behind it is not real or will not change your entire life if experienced. As I put it in an aphorism in a small book back in 1996: ‘Symbols can convey the hardly explainable, but also obscure the original meaning.’