Not tried them myself but i have seen people wearing them, even if not correctly. Seen them around the back of the neck - perhaps they slipped, who knows? The only issue would be if the 'earbuds' fit in the ear properly. I have problems fitting in-ear earphones and they come with different size earpieces. I am in the process of having some 'CENS' moulded earplugs made at the moment so at least they will fit properly.
Personnelly i would rather have standard type ear defenders for the same amount of money or cheaper.
Worth paying a bit more and getting properly moulded passive plugs. I did try the Napier things some years ago, but was not convinced about sound proofing ability. Having lost my hearing about 14 years ago, it is not to be recommended. Bear in mind, one of the side effects of deafness, is the inability to hear !
A friend of mine tried these on Friday pigeon shooting, he is a bit mutton anyway so less concerned about protection than many but left with a headache and will be going back to over ears. Personally I would only use over ear, especially with the volumes involved in clay shooting.