They're probably very good compressors but you need more than a good frigey, also necessary would be an experienced refrigeration engineer and a lot of time and money. Compressor volumetric efficiency data is probably available, but in an aircon system its the coils and fans that have the biggest effect on operating efficiency. You have to look at the overall system rather than individual components.
By the time you design, select and assemble indoor and outdoor coils, fans (with DC motors!) piping, refrigerant control device, reversing valve if you want heating as well as cooling (also DC - good luck finding one), filter assemblies, casings and controls, you could finish up with a beautiful and efficient machine, but my guess is you would be tweaking it until the day you die before you saved a single Watt. The good people at places like Daikin and Mitsubishi would probably assign about 5 R&D engineers to the job to make it work well and then spend upwards of $50,000 on compliance and efficiency testing begore they could market it.
At best a DC unit could save you the inverter efficiency losses, but while those loses are annoying, additional PV and inverter capacity to overcome them will be a lot cheaper than engineering a DC aircon from the compressor up.