Elektron officially supports both the MKI and the MKII, and new OS‘s can be installed on both units. However, some features will be limited by the hardware on the older units.

From the manual: The S/N ratio for a MKI unit outputs is 91dB and the outputs are unbalanced..

32-step patterns.
Output S/N ratio: 91 dB
Input impedance: 100 Ω
Dimensions: 340 x 176 x 68mm (including knobs)
Unbalanced inputs/outputs. 1)

UW specific:
2 MB RAM
2 RAM machines
32 ROM slots

64-step patterns
Output S/N ratio: 100 dBFS
Input impedance: 9000 Ω
Dimensions: 340 x 176 x 63mm (including rubber feet and knobs)
Unbalanced inputs/balanced outputs.

UW specific:
2,5 MB RAM
4 RAM machines
48 ROM slots