I have used these with ski boots. As mentioned in another post, you just need to adjust the bindings. Unless you modify the flex of your ski boots, they will probably feel too stiff when riding a board.
Even with board boots, these bindings can be tricky to adjust for a perfect fit. There is a trick that helps.
1) Set up the "fine tune" toe screw to tighten the bail all the way.
2) Set the toe and heel piece so the heel trips, but does not completely close.
3) Loosen the toe bail "fine tune" screw just until the heel bail closes completely when tripped.
4) Loosen the toe bail with the "fine tune" screw another 1/2 turn.
The last step is the key, and I am trying to remember from a long time ago, so you might need to loosen a bit more on the last step.
Once I had them tuned, they would always snap closed.