As the customer, you have the choice of  OEM (Original Equipment Manufacture) parts or aftermarket parts.  As you might expect, aftermarket components work out notebly cheaper than their OEM counter parts, however, my supplier has assured me that the aftermarket components are of the highest quality.  All parts are supplied with one year's manufaturers warranty.

Note:  A/C compressors should only be fitted by well qualified air conditioning engineers.  This is because, (in most cases) the old compressor may have severely contaminated the refrigeration system and require at the very minimum a full reverse flush of the system including replacement of the filter dryer & expansion valve / orifice tube components.