We’ve only been on SS expeditions and, as stated above, it works differently. There are occasionally more traditional excursions offered (and I imagine there are more of these on some itineraries) and you can sign up for them in advance on the website but mostly you decide what you want to do the night before you do it! The exception is kayaking where you need to sign up at the beginning of the cruise. You then have to attend the kayak safety briefing. You then have to indicate which kayak excursions you’re interested in and they sort out a rota as spaces are limited. We didn’t actually get to kayak at all in the Antarctic (as the weather closed in) but, in the Arctic we got to go 3 times and could have done more than that but there were other excursions we wanted to do. On that cruise we did a mix of kayaking, hiking and zodiac cruises with an extra couple of more traditional coach-type excursions where there was a choice but I think most people got to do whichever they chose.
We love the expeditions but they are very different from a traditional cruise experience. Much more casual and relaxed. And fewer people. But with SS you still have the luxury element. It’s a great experience. We’re off to Greenland at the weekend!! Can’t wait!!