Why are you so obsessed with this "certification"? I've literally never heard of it before. I'm sure the experience is better than not having it, but mouse is right: it's not the type of experience you will use at a firm, so I doubt it's a ticket to a firm jerb.
I have only ever been in one interview. I would have killed to have had something to say other than Times Square looked cool and I was prepared for the LS challenge. I could not even talk about grades because they had not been released. I discussed my desire to work in communications law (to a firm not handling communications law).
My point, short of throwing down a bag full of As and telling the firm they have till the end of the day to make an offer, you best have something compelling to convey. For those soon facing interviews, they would be far better off talking about their learning experiences in the courtroom then those in the classroom. And yes, what one actually learns as a Certified Legal Intern might help close the deal . . after 10 weeks in BL I can say it will not be less useful than what you learn in LS.