Just my 2 cents,,,when my son and I decided to get into racing. many moons ago, 1997, he was 17, ( 800 novice, then expert)), we tried the fad/preferred finger throttle, and we tried the stock thumb, on land, on the trailor, in my garage,,,,,fortunately, we both agreed that the thumb felt better, fortunately because we only had one boat, that I also rode and tuned, later I rode novice when he went to expert.
What we both found was that when you are on the back stretch, pinned, in very rough waters, going 60 mph,,,and hanging on for dear life, to prevent becoming a rag doll hitting the water, at 60 (mph), you are able to hold on to bar with all 4 fingers, and the thumb freely controls the throttle.,,what we both found, is that with finger throttle, you are gripping hard onto the bar to hold on, but this wants you stay on the throttle, when at any moment, you may need to lay off the throttle.
I slightly modified the stock seadoo lever so that the retaining pin would not brake, which is what is going to happen, I made my own metal, not plastic pin to secure the thumb lever,,,,and now, 15 years later that same very tumb lever prevails..your wife, in my opinion, is better off.
I would stick with the thumb, but the stock plastic partial pins will break under continued harsh conditions.,,that happened to us in our VERY FIRST novice
race,
And sticking with stock will save you $'s.
Just my 2 cents.