I have been using ceps for about two months now and find them excellent!
Previous concern about my decreasing hearing has gone.
Tiny problem if your other crewmembers or passengers are on conventional headsets/helmets, they often don't hear the radio you have now turned down, and will talk over incoming radio traffic.
Mine are custom-made (impossible to push in too far) by "Headset services" at Shoreham. u.k. tel: 01273234181
Initial ear moulds can be taken at any hearing-aid shop, (there are plenty out there, didn't see them myself until I started searching.)
Your helmet will need to be adapted though.
For anyone who has hearing that is very close to the limits during their medical this is worth the cost and effort.
Clado