I would rate it 6 stars...

Love the looks!
Love The Animation!
Love the attention to detail, especially using IIII for 4 instead of IV which Ive seen others do which is inaccurate to whats was on old Grandfather Clocks and antique clock faces!
The only thing I woudld like to see is its screensaver setting to actually appear in my screensaver settings so I could use this app to lock my machine.
Brilliant!!!

Editor1979 about Mechanical Clock 3D Lite