Matching a inflatable rigid Zodiac 850 2009 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.
The power gap is worth calling out. Rated to 350 hp, the Zodiac 850 2009 has a 325-hp advantage over the Zodiac Mark I ST 2009's 25-hp ceiling — enough to notice on acceleration and at cruising speed, particularly with a full passenger load.
For family outings this is probably the sharpest distinction between the two. The Zodiac 850 2009 is rated for 15 passengers, while the Zodiac Mark I ST 2009 caps at 5. If you're regularly pulling extended family or a group of friends onto the water, the extra seats on the Zodiac 850 2009 could be the deciding factor.
Bottom line: Choose the Zodiac 850 2009 if your priority is putting more people on the water — it handles 15 passengers and at 27,9 ft it has the deck room to back that rating up comfortably. The Zodiac Mark I ST 2009 is the smarter pick if you want a lighter, easier-to-trailer boat rated for 5 that costs less to run day-to-day.