If you look at the link you will see how it works. Had one for my dinghy and worked very well. As it states it will give you about 30% more push. That is what I needed and worked well for me.

We used them on River Tugs in Philadelphia for a small Tug Barge operation. We could work a 800 HP Tug and do the job of a 1200 HP Tug. Yes they work. Now it depends what you want it to do.

To say they don't work is wrong. Maybe they didn't do what Larry wanted and it didn't work for him. There are comapnies that design them for each outboard and they will do the job. One that in not matched to the outboard will not do the correct job for you.