Seajet2 Live on Map
I traveled between Milos to Santorini with seajet2 in a bad experience. The boat arrived 1 hour late and we didn't have our places to sit, they didn't exist in the boat.
It might me nice if everything works, But in case of cancellation (i.e. due to wheather), they leave you completely alone. No one responsible at the port, no one has information and you are loosing alternatives for your transportation while you are waiting that someone is willing to give you information. Refounding is difficult unless you haven't bought the ticket at the next corner. Conclusion: If you have 4 weeks to travel, theres no problem. If you have more precise plan: forget them.