Now that I have an actual keyboard, a cup of coffee, and the brain is starting to warm up...
Those feeds are so close to identical nutritionally that the only benefit you get from mixing them is a bit of exercise, and maybe a feeling of doing "extra" for your birds. There are tiny differences - but they are so small there no research I'm aware of which would allow me to opine on likely effect for most of them. They are small enough there likely is no measurable effect over reasonable time scales in a typical backyard flock, much less observable effect.
Kalmbach has slightly better disclosed vitamin content, higher fat and fiber. The Kent/Blue Seal has better Phosphorus, Met (barely), Selenium. All are w/i acceptable ranges, some are good to very good for a layer formulation.
The only clear difference?
If you are in an area of the country with known Selenium deficiency, you should favor the Kent/Blue seal. Slightly higher fat content in the Kalmbach - if my birds free ranged (and they do) and I wasn't in a selenium deficient area (sadly, I am), I'd favor the Kalmbach.
If I had to choose between the two this AM, w/ one cup of coffee, not enough sleep, and knowing that I both free range and am in a selenium deficient area? Unless there was a significant price difference, I'd have to try one brand for a year or two, keep some records, then try the other for similar time span and compare. Though I'm favoring the Kent/Blue Seal.