I have a pair of 4% that I decided to buy at retail price. My justification was that I spend A LOT on cycling, and usually only buy running shoes on clearance except for my race shoes which are Nike Flyknit Racer. My open marathon pace is around 6:00 and I have found the Vaporfly to be an awesome shoe at this pace. The main difference that I see is that I am not that sore the day after a very long hard run, and using the Garmin performance condition data, I am usually in the + range when I run in these shoes (I only use them for long marathon paced runs). It may just be a placebo, but even still I’ll take it. I think it will be really cool when other companies start making their version of these.
Thank you for the feedback even if just n+1 
I’m the author of the homepage review.
I will do a second review on the 4% fly, but just some first initial things after a couple of test runs. There are no half sizes so i took size 8 instead of the 7,5 i have in the ‘normal’ fly. That made them much roomier in the forefoot although just a tiny bit longer. So i think they are roomier just by design. The insole is glued inside the shoe and the midsole is much more carved out then with the normal fly. The insole does press a bit in my arch, but it didn’t gave me any blisters so far. The midsole material is different. It is lighter, maybe even softer and it even sounds different. But what strikes me the most is the speed. I just did 6 x 1km with 2 min recovery. Ran 5 out 6 at splits i haven’t seen in some years. And it didn’t even felt that hard, not muscle fatigue wise or in breathing intensity.
They are also less stable due to the more carved sole.
Every non sponsored pro should at least give them a try. They might not work for everybody, but there is definately something with these shoes.
Jeroen