I have ridden several Sportifs including the Dragon Ride, The Cheshire Cat and The Burgess Hill Rumble.Each one was slightly different, due to having different organisers.
A feature common to all was a choice of 2 distances, with the longer distance involving an extra loop. You pre-register for a particular distance, but on the day, depending on the weather (sportif riders are fair-weather cyclists?
), or how you are feeling, you can opt for whatever distance you prefer. They all had signed routes, with plenty of marshalls to keep people on course, and were all very popular, with lots of riders to ride with, whatever your preferred pace. Some give you timing chips, so you get exact ride info. Some are more low key -eg Burgess Hill Rumble had no official start at all last year, though the route was well sign-posted and marshalled.Food available also varies, likely to be mainly sweet rather than savoury, and energy drinks and bananas normally available at the feed stations.
If you have a lightweight race bike eg carbon or alloy with carbon forks, sportif rides are a good way to try riding shorter audax distances at a higher pace than you would normally ride an audax, as the numbers of faster riders and ethos of these events encourage you to go faster than on the average audax ride.
The extra organisation and support you receive (eg sag wagons, doctors, ambulances) translate into more expensive entry fees than what we are used to on more self-supported audax rides.
I can only suggest you have a go at one or two, and don't forget to let the organiser know afterwards if you think their ride could be improved for the following year in any way.