It seems like nearly all the motorcycle accidents I have been to, including one of my own, involve ankle or distal tib/fib injuries. So, protection is my first priority. Most boots put an ankle joint cup on the side and that's all. It is really no protection at all.
Fit: My feet are C width, and Alpinestars are too wide for me; hence, while comfortable, their ability to protect is compromised for me. Sidi fits well for me. The only complaint I have is that the boot is stiff (good for protection, bad for comfort) through the top of the foot and walking and shifting it pinches the top of my toes. Also, the top front rubs on my shin on one foot, but only a little. Problem is solved with taller socks or tucking in my pants. I have only got about 40 hours on them and am pretty sure they will break in some more.
Protection: Without getting a custom made boot this is about as good as I could get. It grips well at the ankle and through the foot, and the calf section is adjustable. I believe that will help with a possible torsion break. The external bracing is rigid without biting the leg or foot.
Durability: Pretty sure they will outlast me. Seem indestructible.
Cost benefit: In the ball park for decent boots, but most boots seem pretty overpriced. Get a lot in the way of protection and durability compared to many boots.
I have mostly positive things to say about the fit and appearance of this boot. I live in SE Asia and ride mainly off-road. The boot has been great for the last 1-1/2 years during both the dry and rainy seasons. However, during the last ride, the heel and upper boot separated! Thankfully, I always ride with a roll of Duct tape! The boots have been well cared for, cleaned and polished regularly and kept inside. I had thought that the lower was sown to the sole and rubberized, but this was just an 'effect' and somewhat misleading. No option available for service on the SIDI site.