My thought process would be that like with most things on paper, they generally look and sound much better than they actually are in the real world. I imagine the tests that the company runs are in perfect conditions to be able to get the absolute best results possible. Another thought that I have on the matter would be, if the Sharrow Props are so great and do everything that they claim to, why doesn't everyone have them? Why don't boat manufacturers include them with every boat that they sell? Why aren't there a bunch of other companies out there making knock-off's, or their versions of the Sharrow Prop's to try and compete or take money/customers away from them? Per their website, Sharrow Props have been around since 2012, of which again in that time if they really were as great as they claim to be, you'd think everyone would have one by now, or at least they'd be much more popular than they are. Also, on the website they have a claim that their props are 9%-15% more fuel efficient than the rest of the competition, which would make the OP's fuel economy of .7 mpg at optimum cruise up to maybe .805 mpg at the best? As I stated before, the very small possible increase in fuel economy wouldn't make me want to shell out $15k for them. I also just watched a video on YouTube of a family adding Sharrow Props to their 37' boat with twin Mercury outboards on it. Their best fuel economy figure was at 4k rpm going 25.3 mph and getting 1.05 mpg with the Sharrow Props. Conversely, with what they call the "Factory" props, they were able to achieve similar results while doing 4,500 rpm traveling at 29.3 mph and still getting the above 1.05 mpg. The time that the Sharrow Props seem to "shine" would be between 3,500-4,500 rpm or I'm guessing when the "Factory" props are struggling to get up on a plane. Other than that though, the "Factory" props are able to get the same fuel economy at a slightly higher rpm and speed than the Sharrow Props.