I ride the Force and have Flux bindings as well. They have 2 very different feels. With the force the basplate has more flex and allows more natural flex of the board, the ankle strap is stiffer and more responsive, and the toe strap is very basic and not very responsive.
The Flux baseplate is somewhat stiff, the ankle strap is more cushioned and less responsive and the toe cap is super responsive. Because of the cush straps they're more comfortable when you're in them for long periods of time.
The flux take longer to strap into because the ratchets dont slide down the ladders as easy as the Union ratchets do and the flux take longer to tighten because they're softer, where as the union have less play and are tight almost on contact with the boot.
Really it comes down to preference of feel and fit with the binding.