Which features matter before buying a PST to VCF converter?

I have an Outlook PST file that contains a large number of contacts, and I want to convert them into VCF format so I can import them into my mobile phone and other email clients. Before purchasing any PST to VCF converter tool, I want to make sure I choose the right one. I am confused because many tools claim to offer the same features. Which features should I check before buying a PST to VCF converter (such as accuracy, bulk conversion, duplicate handling, or compatibility)?