Heel lockdown in the Clifton 9 is excellent, with or without a runner’s knot. The ankle area and heel tab are very well padded so comfort around the rear of the shoe is top-notch. There’s still an elf heel tab which is very 2020.
The upper is made of an engineered knit mesh which doesn’t feel like a knit at all- there is no stretchability so it’s of the utmost importance that you order the right size. Breathability is better than the Clifton 8 due to the knit mesh being thinner.