Star Clippers has 3 ships, 2 that are exactly the same (Clipper and Flyer) and the Royal which is about 50% bigger.
They are a tall sailing ship, and unlike some of their other competitors they are not automated, like Wind Star or Club Med cruises. They do have some great itineraries, as they are smaller ships they can get into places that can't handle the bigger cruise lines.
They have a larger number of repeat customers, and offer good deals to them. They also do a lot of lecture series. They do have a heavy European mix, their announcements are often in 5 languages.
When I went on it about 10 years ago, I was on the Star Flyer (I think but I'd have to go back and look) I did from Mexico down to Roatan. I found the cabins good, the food mixed (at best, they are are trying to be too many things to too many people and it just makes for a bit of failure), I enjoyed the uniqueness of a smaller sailing vessel, and the people were interesting. I did find there were a lot of European smokers. Don't know how much that is changed.
I went solo on an indepenent FAM trip to try it out. I moon-light as a travel agent, and have been for over 25 years now.