Definitely not a gimmick. They work as advertised and are great to have with you at any event (concert, club, etc) or when you're cutting the grass, or near a jet engine, or any time your ears will suffer from an exposure to high dB levels for any extended period of time.
At one time I did a mini review of the ER-20, and shared my thoughts in terms of how well/evenly they attenuated the volume of my main 2 channel audio system. I did some experiments listening at 90-95 dB with the ER-20 in my ears, and compared how it sounded relative to listening at 70-75 dB without the ER-20 in place. The results were remarkably similar, suggesting that you can confidently wear the ER-20 while attending a concert or out clubbing and be assured that you're not hearing a (much) distorted sound, but rather just experiencing the same event at a safer listening level.
Do an search on ER-20 for threads with ER-20 in the thread title (you'll have to use the advanced search feature to accomplish this, but it's easy, give it a try). You should find several informative threads, including the one I've mentioned above.
