Hi Cheap,
The Prometeia 2 ST is a cut down version - it offers r134a and NO LCD or USB.
The Prometeia 2 is the standard unit offering r134a and LCD and USB.
The Prometeia 2 GT is the top end official unit offering r404a and LCD and USB.
Then there are my custom units offering r507 and better cooling heads, SLI units and waterchillers.
They are all pretty quiet and can all be controlled via the software (apart from the ST model).