As you’d expect for the price, the Avenir’s soles are made of a carbon-reinforced glass fibre and nylon composite. They’re lightweight but not that stiff under aggressive efforts. The rest of the time the slight flex doesn’t show and you can enjoy the great comfort.
The upper is really pliant and shallow, especially in the toe box, so you get a snug fit. The so-called aero ratchet struggles to get that last click of tension for a tight fit though, and doesn’t have a one-step release. It isn’t that aero either. The supplied cleat bolts are 4g lighter than Shimano’s but are also a bit softer, so try to go easy on the torque.