jqderrickThe ones you are talking about are basically sponges. While those types will attenuate sound, it won't do that well at maintaing any sort of sound quality. This type of earplug isn't there to block sound so much as is it is to reduce the volume. I know this sounds picky, but the difference is important.
PeacefulKancer@jqderrick, @PeacefulKancer is right about the sponge style versus these. I haven't used these specifically but I switched from the sponges to musician earplugs for concerts and they are a huge difference.
Any dB attenuation rating given by the manufacturer should be accurate, albeit not necessarily certified. With that said, any noise reduction factor is going to be given in ideal circumstances - in this case probably the plug smashed nicely into a round tube. Your ear canal however is not a round tube so it may not get the ideal dB noise reduction factor as given by the manufacturer. Furthermore, the end user may also not install it correctly, so that will again reduce the rating.
With that said, I don't believe that these are for saving your ears. They are meant to reduce volume. So when you go to a concert it will reduce the volume when you are in the front row but the sound could still be loud enough to damage your ears. If you are looking for hearing protection, I would suggest getting actual hearing protection or doubling up.
Edit: The 3M earplugs for a nickel are the ones that I first mentioned. Those are sponges and will have some sort of sound reduction associated with them. These do too, however, those are ear plugs, these are not ear plugs. Again, if you want to protect your hearing get earmuffs.