I went with my family to visit the Jurassic Coast with this fast boat. The trip itself was great, the kids enjoyed it a lot, though one of the two had a bit of motion sickness. We were lucky, it was a beautiful day and the sea was flat, I am not sure I would go with a rough sea. 90 minutes is just enough, the view from the boat is fantastic, the ticket is quite expensive but it's aligned with the high prices of attractions that you find around England.
Just a remark, we didn't understand much of the explanations from the crew member, we are foreigners and he was speaking too fast and with some strange accent. Perhaps a booklet with multilingual translation would make this attraction more suitable for non-English tourists