These wheels tick all the boxes in terms of low weight, good aero, good braking and relatively reasonable cost. I've used them in several crits plus a few longer events. Braking is very good, maybe on a par with alu, but hard to say. On a long ride I descended one of the more challenging hills in Malibu (Deer Creek) and I had no problems with overheating or loss of modulation. I'm very happy with these wheels. Maybe the high-end Zipps or Enve's are better, but I'd be surprised if the difference would even be noticeable for most of us amateur riders.
Mid to long rides and a little bit of racing (crits). A real smooth ride while at the same time super reactive. and very fast. I highly recommend these wheels!
Note that the Yksion tires that they come with are very grippy and have low rolling resistance - they too will make you fast.
However, these tires are very fragile and the Mavic fluid that comes with the tires is not the best (by Mavic's own admission!). That said, the Mavic support is very good. Do read up on tubeless - if that's how you will use these wheels (you can always fall back on an inner tube - but that's losing some weightspeed advantage).
