a jet d
a jet drive is one of those things that you don't get unless you absolutely need one.
They are designed to run in very shallow water. The technology is exactly the same as is used on a jet ski. Water is pushed out of the (jet) by an impeller to create forward movement much the same way a jet engine on a plane blows pressure out of the back of it's engine.
Much the same as you would use different pitched props on a conventional motor, there is different impellers depending on the particular application.
A jet is a total gas hog often guzzling up to double what a conventional outboard would at the same displacement. I didn't say horsepower because if you take, say a 60 horse and hook a jet drive on - bingo, now you only have a 40 horse jet - about 1/3 of your inital horsepower is gobbled up in order to drive the jet.
So if you want to see your fuel costs near double and turn your 115 into about an 80 horse and drop a couple of grand on the lower unit itself - plus re-rig it - then a jet may be an option - but unless you are running in water that is only an inch or two deeper than the draft on your boat with the motor up there is absolutely no reason to run a jet..."
A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it :)