I think you would have to create them yourself to be the most effective.

Programs that embed subliminal affirmations such as HoloSync insist that you speak them yourself and they embed them for you for this reason I think - and it also happens to be a highly effective marketing technique in putting you off using other people's recordings, so you have to buy your own :)

The reason I think it has to be done in your own voice is that otherwise you may not feel the affirmation applies to you.

If I came up to you personally and said "I am very happy", you would automatically (consciously) assume that I was talking about me, not about you. So I'm guessing the same thing applies unconsciously also.

If instead I said (in my voice) "You are very happy", there would be no confusion.

I think the kind of recordings that the (very funny) ad is referring to are those where the instructor on the recording tells you what to say, hence "Repeat after me, I am the best" in the first scene...so you still hear the affirmation in your own voice.