A mini-suite on this class of ship is essentially a larger version of a balcony cabin. We had one booked on Norwegian Jade, yet accepted an upsell later on, so we didn't actually sail in one. I looked at it out of curiosity, and it seemed nice. Note that you don't receive suite benefits for this category.
If you do decide to book, check the deck plans so that you're under a quiet area rather than the Lido or other areas from which noise might be bothersome.
If it were me.... I'd do it, for a different experience.