I'm on Jet6's and 9's. I use my dual Jet 9's about 98% of the time, so when I TT keep a disc cover on my rear Jet 6 and use the Jet 9 front. I couldn't be happier. I've owned the older HED lenticular, Renn 575 and a Zipp 900 and I am equally as happy with the cover for $100. Taking off is a bit of a PITA, but it's not terrible. My training is way off from the past year so I can't compare splits. Seat of the pants I feel no difference with the wheel cover and the first TT I did this year with basically no training(and pneumonia) I was still moving at a good clip.
My vote is disc cover and if you TT near 25+, the Jet9. Below that, the H3 shines in high yaw angles.