Matching a inflatable rigid Zodiac Cadet RIB 310 2010 against a inflatable non rigid Zodiac Mark I ST 2009 means you're likely deciding between two genuinely different on-water experiences. Hull type shapes everything from ride quality and fuel burn to dock handling and resale trajectory.
Both boats share a closely matched power ceiling — 15 hp for the Zodiac Cadet RIB 310 2010 and 25 hp for the Zodiac Mark I ST 2009. Real-world performance will come down more to which motor is actually bolted on, its load at the time, and whether it's a 4-stroke or 2-stroke setup.
For family outings this is probably the sharpest distinction between the two. The Zodiac Mark I ST 2009 is rated for 5 passengers, while the Zodiac Cadet RIB 310 2010 caps at 4. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Zodiac Mark I ST 2009 could be the deciding factor.
The Zodiac Cadet RIB 310 2010 has a documented top speed of 24 mph. Speed data wasn't available for the other model.
Bottom line: Choose the Zodiac Mark I ST 2009 if your priority is putting more people on the water — it handles 5 passengers and at 11,5 ft it has the deck room to back that rating up comfortably. The Zodiac Cadet RIB 310 2010 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 4 that costs less to run day-to-day.