I purchased these boots for summer riding, in the Southeast. I will break this review into three parts. 1. Fit, 2. Function, and 3. Overall Thoughts.
First, about my foot. ankle, and calf. I wear a size 12 in nike/asics/brooks, or whatever other standard running shoe brand. My foot is narrow and not very thick from top to bottom. My ankle bone area in also thin. My calves are thinner than most, as well. Typically it is difficult to find snug fitting motorcycle boots because of my foot and leg's thinness. I ordered these in a size 45 ( I also wear a 45 in Sidi Crossfire 3 SRS, for any dirt guys comparing). If these boots were any shorter, I would have to size up. I would typically never be ok with a shoe having so little extra room, but once on the bike, I have no issue with rubbing my toes on the end. (Like any piece of gear, try it on, on the bike) For comparison, I have a pair of Dainese Torque D1 out air boots. I wear a size 44 and they have slightly more room, length wise, as do my size 45 Crossfire SRS . The Dainese fit a little more snug around my ankle. That is the only area in which the Dainese is better. The adjustments on these boots are phenomenal. Having small calves, boots often lack adjustability here. With my leathers on they snug up nicely, but still offer tons of room for larger calves. As mentioned, the ankle is pretty roomy, and the foot bed is wider than expected from Sidi. One could add a slightly thicker sock, and it is not longer an issue.
Before I dive into its actually uses, let me just say these boots are badass. They are beautiful, and look ready to perform. The airflow in the boot is amazing. As I mentioned previously, I have a pair of Dainese torque d1 out air boots. They do not flow half the air that these do. I have about 400 miles of mountain road riding on these, so far. Returning home on 90 degree days, while wearing leathers, my socks are completely dry. The coolest I have ridden with them would be in overcast, damp low/mid 60's and my feet never felt cold, even though I had all of the vents open.
These are roughly 1/2 inch taller than my Dainese boots. They feel much more stable and secure than the Dainese's, as well. These feel more like a high level dirt boot, in terms of support. However, these are insanely comfortable and flexible right out of the box. I wore them around the house, twice, for about 30 minutes just to check everything out. I never felt there was a break in period. The soles are grippy and confidence inspiring, but still stiff. Peg and shifter/brake feel is great. I would not want to run a marathon in these, but they are comfortable off the bike to walk around for a bit. I noticed significantly less side to side flex in these vs the Dainese, which was my chief complaint with them. I want to know my ankle is secure, while riding. Putting these on, and removing them is super easy. When tightening, going from the top, down, seems to work best for me.
3. Overall Thoughts
As with all Sidi products, the Rex Air is a top notch boot. It does everything it is advertised to do and looks great doing it. Yes, they are expensive. If you are lucky enough to see them on sale, buy them immediately. If you are on a naked/sportbike, doing spirited street riding or track days, these are the ticket.