I come from the Kinvara 10 and I can say that they are quite better. They are a little tight but I consider it necessary especially for safe sprints. They fit perfectly on my foot with summer socks. They are very comfortable even though I have used them so far for just over 5km - 30min per session. I also have the ultraboost 21 but I believe it is a very different shoe to compare them. The activity tracking feature is the best. I am very satisfied.

Είναι πανέμορφα . Δυστυχώς τα επέστρεψα πίσω καθώς έχουν σκληρό πάτημα συγκριτικά με τα ultra boost της adidas και τα Nimbus της Asics. Ο κύριος λόγος που τα επέστρεψα ήταν ότι δεν ένιωθα σταθερό τον αστράγαλο στο περπάτημα .( Δεν τα δοκίμασα καν στο τρέξιμο ) ελ
Είναι πολύ ελαφριά και πανέμορφα αλλά με τα ίδια χρήματα πας σε αντίστοιχα πολύ καλύτερα μοντέλα της acics Nike Adidas

Being a runner of short and fast distances for many years, I have to say the following:
A) The shoe is beautiful, it resembles the ultra boost a bit but personally, it doesn't bother me.
B) It is convenient and comfortable. You feel like it gives you a sense of propulsion.
C) It has an integrated Bluetooth chip. You download the corresponding app from the company and you can see various measurements, such as kilometers, pace, heart rate, etc.

The only negative thing I can find is that, like most shoes in this category, it lifts the heel quite a bit, resulting in foot issues after prolonged use