I received the Vertical K's on February 28th and when I pulled them out of the box, I just could not wait to get them on and hit the trail. They are feather light and very flexible right out of the box. I could tell that they would not require the break in time that other shoes, even minimalist, would require. Once I slipped them on, they felt almost slipper-like and I was slightly worried about the support in the upper for off camber trails. I was worried that my foot would slide around. The heal cup felt good and stable. The lacing was the easiest I have tried from Sportiva. It was very easy to get the right tension on the laces throughout their span. This, I could tell, would be beneficial in ultras with shoe adjustments.
Once on the trail, the traction and cushion were the first two items that impressed me the most. Most of my training runs start on a very steep half mile gravel road stretch. Unlike other minimalist shoes I have tried, I did not have the issue of rocks rolling under each step. The Morpho-Dynamic "waves" really help to grab the trail. They also allow the sole to flex, providing more cushion and eliminates the need for a rock plate. On the down hills, the cushion really was nice. Don't get me wrong, these are not some bulky, thick-soled shoe. These are a low to the ground trail racer. My next test was single track with some off camber sections to test out foot movement and roll. I was extremely impressed that my foot felt so secure. The reinforcement stitching on the upper really holds your foot in place.
I have put about 85 miles on these shoes so far and the wear is very minimal. The first trail race I did in these shoes was a great success. I also completed a very technical trail marathon this past weekend with rain for about half of it. The shoes held very well on the wet rocks.
All in all, these have become my go to trail shoe for both training and racing. Although I have not taken them on anything past 26 miles, I will not hesitate to do so. One suggestion I do have to anyone considering these is to go up a half size to a full size.