I never got to try the Kinvara 3, so going into this test run was a good experience, having no prior experience in the shoe, it gave me a fresh outlook, and nothing to really compare it to.
I've always been a fan of the idea of the Kinvara, so when I was given the opportunity to take these out for a spin (even if it was only for an hour) I was very happy. Putting them on was great, however there is so little to them it took a little playing around with the laces to get them to fit nicely. But once this was done, they were secure enough that they didn't slip. They were an odd feeling, as the upper is so light and flexible it almost feels like something is missing. I soon got used to this, and it actually feels quite good. And at only 218g for a size 8, they were very light. Initial thoughts were very good (I got to try the fluorescent yellow ones, so I was impressed with the design too!)
The midsole is made up of high abrasion EVA with an upgraded Heel insert, going from ProGrid (as seen in the Kinvara 3), to Powergrid. Having not tried the Kinvara 3, I couldn't tell you if this is a good change, but they certainly felt plush whilst walking on my heels, and even when running, the occasional heel strike did not cause problems. The 4mm heel drop is certainly noticeable if you are used to a higher shoe, however the entire midsole is relatively thick for a minimal shoe, so they felt great. The midsole was also very flexible; in part due to the lack of a traditional outsole, but also because of deep flex grooves.
The upper uses a lightweight mesh, and Sauconys FlexFilm for added support and comfort. The idea behind this is that the FlexFilm is heat welded onto the upper, reducing the need for stitching, therefore making the shoe lighter, yet just as durable. And the result is exactly that. They are very light, and very comfortable. The shape of the shoe is just what you'd expect from a minimal shoe; fairly wide at the front, but snug enough around the laces and heel. And speaking of the heel, again, you can see here they have saved weight. The heel has a very, very light counter, that is so flexible that it almost isn't there, and has 2 memory foam inserts that hug you either side of your achilles tendon. This actually felt great, and you didn't notice how little there was in the heel. One thing I will note however, is that the tongue is very thin, so you do have to be careful with how you tie your laces. Once I'd played around, and added butterfly laces however, this did not cause further problems.
The outsole is very minimal. It uses XT-900 rubber that is relatively sticky, and hard wearing too. The triangular lug pattern is designed for flexibility as well as saving weight. The lugs are also supposed to act like pistons, however, I did not notice anything specific regarding this. They a certainly light and flexible, however my one concern abut this, and indeed one concern about the shoe as a whole, is how this would respond to a slightly inefficient technique.
I really enjoyed my run in these. A lot of it was technique based, which was a great session to test these shoes out for their intended purpose; i.e. that they are a minimal transition shoe. They are definitely easy to run in, and I can see how they would be easier to transition to a more midfoot style than a more traditional shoe. The fact that they are so light means you can effortlessly pick up your feet, and turn them into the next stride. The 4mm heel drop definitely made my calves work. So much so that I am still wearing my compression socks as I type, hoping that they will help ease any aches I might feel in a couple of days. Fingers crossed.... However, calf ache is a good sign in this case, as it means they are getting worked in the correct way, and will begin to gorw and adapt to a more minimal shoe and more minimal style of running. All in all, these shoes are fantastically comfortable, and tick pretty much every box I could think of within a 1 hour time limit. As I've said, my only concern is that the lack of outsole may mean they wear out a little quicker than a more traditional shoe. But take things slowly, and transition into these, and I think you'll be onto a winner