@Goblin, a person whom I've recently learned to trust, swears by them. On his praise, I have some ready to plug into my trusty Feather DX as soon as the current blade is past its prime.
Well, we are all different - I hope they live up to my hype!
I haven't gotten around to more shaves with the Kai Captain yet. I had 3 AC blades loaded in different razors and am finishing them one at a time, also mixing up with other formats. Having initially shaved with a fresh Kai, fresh Schick (and then a Feather Pro) back to back I still think the Schick is smoother and the Kai is a little sharper.
Sharpness: Kai > Schick > Feather Pro
Smoothness: Schick > Kai > Feather Pro
Feather Pro Super was a disaster for me (although I will try it again as I still have 18 left) and I don't like guarded blades.
I reserve the right to change my mind with no prior warning.
In reply to @Dimitri, it definitely will take time to develop the technique enough to get a shave that will rival your DE, but it can be done. Do keep practicing and join the SABRE and shavette SOTD threads for help and encouragement.