The salomon custom shell only works on part of the shell, while the vaccum fit is 100% moldable. It ankle can change, the instep can change, you can even do a cuff alignment when doing the vaccuming process.
It is literally 100% custom to your foot. But yes the flex is softer than what you would expect ( you have to go with the race version to get a boot that feels like a proper 130 flex)
If you can't afford it (which most people can't) it's best to go with whatever fits your foot.