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Safeguarding naive users against erroneous reporting from not knowing the statistical assumptions underlying a given technique i.e. I am agreeing with Nicholas Kogan.
After that, the order of importance of features depends on the use, and on who the user will be. The system does need to cover the whole workflow life-cycle. Fortunately, most of the widely-used systems do offer that.
Ability to import many different data sources across platforms. Reliable name in the industry. Good knowledgeable support staff. Good GUI. Good presentation ability.
Methodological transparency with accessible evaluation tools to prevent the black-box effect.
Ease of use to do cluster analysis as well as anomaly and dependency detection.