I first saw these at a granfondo in the Assos truck. I tried them on, and really liked that the carbon sole extended around the heel, which felt very stable and good for power transfer. Assos actually offered a pretty good deal on them, which I subsequently wished I had taken. Fast forward several weeks, during which I dealt with some serious delay on a pair of Vittoria shoes I had already bought at a huge discount from Europe. A CC rep told me that the Lake CX402 shoe is virtually the same as the Slipper at a lower price so I bought the Lakes. They were definitely not the same shoe - felt and fit much bigger and bulkier than the Assos, and the quality was not of a $500 shoe - so I returned them, and decided to just get the Assos.
The shoes have a slightly bulky look to them from the top compared to Sidis for example, but look quite "slim" from the side. The carbon sole wrapping around the heel makes the shoe very profiled from the back.
The shoes are probably best for narrow to medium width feet. The toe box is quite generous, but the midfoot, and especially the backfoot, are rather narrow. That part of the sole is moldable, but I'm not sure whether it would widen enough to accommodate very wide feet. My pair fit me perfectly right out of the box so I have not messed with "cooking" them in the oven.
The shoes are very stiff, which is great for power transfer, but can make the shoe a bit uncomfortable when unclipping at a red light and putting your body weight on it since the sides are made of carbon. I believe some of the internet reviews I have seen complaining about the shoe being uncomfortable have something to do with the fact that the sole wraps around half of the foot. I personally certainly feel the shoes are supremely comfortable.
The boa closure system is the best I have ever used. I finally got the Vittoria La Tecnica shoes also with a boa closure system, and the Assos' closure is far superior to the Vittoria's.
Cons: the leather around the ankles had yellowed for some reason. It's a pure cosmetic gripe, not functional, but it certainly warrants criticism for a $500 shoe.
Verdict: Top of the line shoe that's as good as it gets in terms if looks, functionality, and technology. If you can afford it, you won't regret it.