In my grumpy opinion, Blue Star Positano was the only thing that made Positano worth seeing. I HATE places that are over-run with tourists like me, so being able to see Positano from the water (away from other tourists like me) was wonderful. There's a reason that so many stupid tourists like me come to the Amalfi Coast, and that's because the views, the experience, the everything are world-class.
Even better, they stop for snorkelling, which was a surprise highlight of the trip - the water is crystal clear, and fish are everywhere, just inches from your face.
Something to note, though: Their group day-tour to Amalfi is advertised as having time to go up to Ravello, where the million-dollar panoramic views of the Amalfi Coast are. The reality, though, is that your only chance of doing that in time is to take a shuttle that runs back and forth between Amalfi and Ravello (not through BlueStar; cash only). Our captain even said there was no way we'd have time. Fortunately he was wrong; we had plenty of time. Just take the shuttle; NOT the public buses.
If you're on the group tour as I was, when you get to Amalfi, they give you a choice: They can drop you off in Amalfi, or they can take you to a private restaurant to eat, accessible only by boat. For some reason, no one else on our tour wanted to see Amalfi (the whole point of the tour in my opinion), so I felt like my family and I were inconveniencing everyone that they had to come back and pick us up (which again, I thought was the whole point of the tour).
Anyway, they provide a fantastic experience that delivers everything as advertised, with prompt communication from beginning to end. Just be prepared to be savvy getting your shuttle in Amalfi as you battle your way through the hordes of tourists (like me). And when they give you the choice of Ravello or the restaurant, pick Ravello. The restaurant is mostly just an Instagram check-in, and you deserve better than that.