Some work some don't.
It's found that if you can make out a voice when it's loud enough you've got a subliminal that has the better chance of working. If you can't detect a whispher... it's questionable if it will work.
You do need to see the list of affirmations that are on the recording to deterimine if you agree with them or not. I've seen some that had suggestions stated in the negative which means you'd get opposing results.
Most of the problems I have with subliminals is the masking music is so utterly boring I can't stand having it going in the background... I'd prefer the affirmations without the mask. If you have to listen to something every day for 30 days. It needs to be provide a little bit of enjoyment.
Alex