This is not something new. I took the course and exam back in 2000. It was sponsored by AWS but conducted by Hellier Associates. The course was very informative. I thought I knew everything about film interpretation, but they opened my eyes. I found the cert to be very beneficial. There is a lot more to interpretation than indentifying indications and indication accepatability. You must also judge film quality. That is a big problem in the industry. You must also, as an interpreter tell the radiographers how to improve their technique to improve film quality, when necessary. Increase exposure time, source to film distance, etc., just to name a few. Also if there is a dispute regarding sensitivity, how do you resolve it? I highly recommend you take the course. Being a CWI does not qualify you as a film interpreter. Sorry, I know you CWI's don't want to hear that, but it is a fact! It helps, but does not qualify you alone. Understanding welding and understanding radiation are two different things.
I am a CWI, by the way. But it doesn't qualify me as an interpeter.
The cert also lends credibilty when resolving disputes regarding film interpretation.