I am a lifelong Alpinestars wearer and decided to take a chance on the Sidi Vertigo Corsa AIr boots. The boots are attractive, in a robotic/ Janet Jackson rhythm nation tour sorta way. They're adjustable in two places, in the calf and above the arch. The adjustments are done by attaching a plastic clip to a metal ring and turning a knob that tightens a piece of filament progressively. The Calf adjustments are done in the same way, but the filament is hidden.
The boots fit snugly at the arch, for the wide of foot and the adjustability makes them comfortable everywhere else. They fit over my leathers easily, thanks to the adjustability of the calf. Walking in them is easy, but they are stiff.
I took them to the track to test them out. When hanging off the bike, the bracing around the ankle didn't allow me to turn my foot enough to not drag my toes while cornering, one time, hitting the ground so hard that it upset the suspension. To adapt, I had to turn my leg more at the hip. This was uncomfortable, but did the job.
These boots will probably crash very well and I'm sure will prevent many ankle injuries. If you want the utmost in safety and are prepared to endure the required adjustments, I would say go for it. Make sure to try them on first. They're not for everyone.