They're talking about the signup process basically. Mint is a terrible product with a fantastic signup process. All those posts about how great it is are from people who signed up, looked around for 5 minutes, then never used it again.
Plus almost all of the users that do stick around go for the high-end financial referrals that Mint pitches them based on their data. Cost Per Action fees for rewards cards and mortgages are through the roof for complete signups of high-value people.
Their conversion rates are terrific even when you include the vast majority of people like us that sign up and never use it again. They were making quite a lot of money when they were acquired.
I have no idea what people are talking about when they fawn over Mint's user experience.