To provide security autonomy capability, such that different users can have independent variants of the encryption algorithm, MK-3 is designed to be customizable. Two levels of customization are supported, Factory Customization and Field Customization. Customization is done by modifying functions and function parameters in the algorithm to yield unique cipher functions while preserving the algorithm’s cryptographic security. The main goal of this work is to present the results from the statistical analysis of the customizable MK-3 encryption cypher, focusing on field customized mixers. We recall the main components of the MK-3 algorithm and overview a subset of available factory and field customizations for MK-3. We test the main instances of the field customized versions and give a general argument for their desired statistical properties expected from an encryption cypher.