Welcome moshe515... [smiley=thumbsup.gif]
The Lux is a "Stepped" grinder while the Iberital Challenge is not, being infinitely adjustable or "Micro-metrical". If youre only making espresso coffee, then the Iberital is the best choice as it allows you to make very fine adjustments to "dial-in" for the perfect espresso. On the other hand, if you brew coffee using more than one brew method that requires large and rapid adjustment of the grind setting then the Lux is more suitable but tricky to dial-in for espresso as each step change results in pour time changes of 6-7 seconds per step.
All the best :)