Ivo's web pages are not the best thing about his business. . . I bought IvoProps for both of my Kitfoxes and found them to be very reliable and efficient. It is the prop recommended by Murle Williams and all the Kitfoxes, that I know about in the Phoenix area (and I don't know them all), are using the medium 3-blade IvoProp. The first Kitfox I built had a Continental O-200. The current Kitfox has a 912uls, both rated at 100hp and I used the medium 3-blade prop on both. My first prop was ground adjustable. This time around, I did buy the IFA and had to send the electric motor back to be rebuilt after 32 hours and during these hours it was used very few times so I was disappointed with it. To the point, the ground adjustable prop would suffice for my purposes and if the electric motor dies again, I'll likely just use the ground adjustable mechanism. I was warned about the IFA motor reliability by one of the locals but, I didn't want to have to deal with the multiple adjustments to find the sweet spot with using the ground adjustable mechanism. As far as how much horse power the medium 3-blade will handle, Murle used it on his first KF-5 which had a Rotax 914 on it so I'm thinking it would work safely on the 912Is but you should give Ivo a call and talk with him if you want the most accurate info.