Dynamic data masking is a great product and solves some niche problems that come if you need to do certain testing with live data at the application level. You should, however, beware of using it as a database-level security device.
I haven’t yet used it in testing because I don’t have the problem that it solves.
The problem that it solves is for people doing testing, especially user-acceptance testing, of an application using live data. It is good at masking data where the user is unable to make direct access to the database to execute queries.
Phil has code to get around credit card numbers, and I will say that he’s not the first person I’ve seen do this. Dynamic Data Masking is not a general-purpose security solution.