The seadoo pumps are pretty efficient and you can't eliminate all cavitation from a jet pump.
They might change the thrust a little bit but it isn't something you are really going to notice. I am not saying they don't do anything but they are not going to be a huge improvement that is going to change your boat.
From the post you linked to.....
"THE RESULTS
I love those cones. Have not done any tweaking or tuning at this point (here, with the new boat), just installed the cones using all 3 spacers provided and ran around a bit to see how it feels. Hard to describe the effects, but the boat handles "tighter" and accelerates better There is no way a pump cone is going to do anything to the handling of the boat as it has no influence on the hull. , which is due to improved pump loading The cone has no influence on "pump loading" as it only influences the flow after the impeller. Top speed and RPM are the same, If top speed and rpm are the same then it isn't loading the pump or impeller at all because if you were changing the load on the pump at all you would have a change in rpm loading the engine more. but speed can be improved by tuning the cone and the impeller/venturi. I have NOT done ANY tuning here, yet the boat runs noticeably better with the L13 (strait out of the box) than w/OEM cones."
In my opinion this is more of a case of I spent money on a performance part and now I "feel" it's faster. Show me the raw data of acceleration time and radar speed improvements then we will know if it is snake oil.
When you change the volume of the venturi of the pump nozzle there is a trade off, you are going to either loose acceleration or top speed, there is no product that is going to give you both.
You would be much better off deciding what you want out of your boat and changing the impeller to match. If you want an all around general boat then keep the stock impeller, if you just want to pull tubes and ski then get a lower pitched impeller for pulling but you will loose top speed.
