I have the adjustable, and am very pleased. This model costs more in the new equipment aisles. The other blades are actually cutting wheels, I believe. You push a lever and pull one out of the base unit and put another one in and push the lever back. They also sell shredding disks/wheels that can be placed into the base the same way.
If you pretty much use one thickness of stuff anyway, then that is probably a feasible choice. I used 3/8 as my preferred thickness for onions, peppers and mushrooms, so that could work for me if I went that route. The adjustable gives me more flexibility for potatoes and such if I want a wafer thin for potato chips or chunky slice for a baked something or other.