ULS2 is currently the basic "912ULS" in North America, there is no 'ULS1' configuration offered.
Differences between UL2, UL3 and UL4 have to do with the gearbox and propshaft parts.
"2" is set up for fixed pitch propeller. The "3" & "4" are variants allowing for constant speed/fixed speed/governor propeller systems.
See the 912/914 series Illustrated Parts Catalog for details...