Eco flow will never go totally even without a lot of fuss and muss, I've gotten it to work somewhat well out of necessity because of the color needed.
As for the Fiebings, if your using the spirit dye, you can get an even color (with practice) in a couple of ways. I've heard that dampening the leather well with water and swirling the dye on quickly will work. I haven't tried it but I've seen the results. Another is a touch of mineral oil on the dauber, swirl a touch of oil on the dauber and dip it in the dye then swirl it on the leather in concentric circles, evenly and quickly. It will look uneven at first, but will dry evenly.
The best overall solution, and a little more expensive, is the Fiebings Pro Oil dye. It goes on evenly. Use the concentric circles and swirl the dye on evenly. Try to get enough in the dauber to not have to stop in the middle of the project to reload. The dye slowly lightens and evens as it cures in.
Do not use back and fourth motions, you cause stripes that way, always use the swirls that overlap a bit.
Hope this helps a little.