I have both the flux sf45, and union custom house pbr.
I will admit the union rackets are just awful, and the toe strap will fit some boots amazingly and some boots just won't fit. I have nike kaiji and they actually fit the toe straps really well. Even with all the union flaws, the union bindings are actually my go to bindings. I just like the feel of the contacts binding.
Flux bindings are super comfy, they kind of feel like pillow on your feet.