yeah, i know the krypton is a 3 piece shell. i assume the spk is a 2 piece, which makes the fact that they have 2 buckles mind boggling.
here's the difference between the two:
2 piece shells flex essentially evenly in 3 directions, forward, left, and right.
3 piece shells flex differently in the same directions. fore and aft, they are relatively soft, depending on your defenition. laterally, however, they are as stiff as many top-end race boots you will come across, giving you the performance you need, but also the tongue softness that makes skiing park a whole lot more comfortable. plus, the dalbello comes with two footboards, one hard and one soft, and two tongues, one hard and one soft. so you can essentially switch the boot from a park boot to a backcountry charger in seconds.
i think you can probably tell which boot that i prefer.