Haven't tried the aviation specific sets but if the dB level is not reduced I would want my money back!
Depends a lot on what you are flying as to how much of a difference you can expect. Varying ambient noise levels an so on.
One of the pilots here on the Air Ambulance swears by his earbud-type ones that he wears under his helmet. I have used shooting-type ANR defenders (Peltor Sport-tac) when flying in noisy military aircraft with good effect and many people use the Bose Quiet Comfort series for their iPods but this is for SLF and not for aircrew. The shooting ones are more designed for the high intensity pulses from shooting rather than the constant background noise of flying.
In summary, they should work and make a difference. How much of a difference depends on what you buy and how noisy your aircraft is to start with. Is there anywhere you can 'try before you buy'? Bear in mind that the dB scale is logarithmic based and so a single dB change is quite a large change in noise!
HTH
BTD