open prop.
But if it were me and I was getting a pontoon, it's hard to beat the durability and simplicity of aluminum pontoons mixed with an outboard motor.
The SeaDoo has some sort of composite pontoons, and then because they oddly stuck with a jet ski style control system, they've had to add some sort of digital cruise control to make it operate like a normal boat. That's just another part to go bad. Then you still have to worry about winterizing the motor and wear and tear on the impeller and wear ring (which I hope isn't plastic on the toon like it is on their jet skis).
Now, if it's a safety thing and you never want to have to worry about your kids or grandkids getting sliced by the open prop, I get that. There have certainly been too many deaths for that reason. But if you're just looking for a good value pontoon, that's not it.