Here are my impressions and comparison testing on three of the top headphones out there for sale: Timberwolf Howlers, Grey Ghost NDT's, Killer Bee Wasps.
1) Timberwolf Howlers----For outside noise reduction the Timberwolves are the best. They reduce noise noticeable better, but the all-metal mode threshold audio is a bit muffled. These I use mostly for noisy locales, or on windy days. I can tell an obvious difference in outside noise reduction using these headphones.
2) Grey Ghost NDT--- Good noise reduction, but not as good as the Timberwolves. Much better than the Killer Bee Wasp noise reduction though. The threshold is just a bit more clear and stronger than the Timberwolves, very close to the Killer Bee's at the LOWER audio levels. These also come in a choice of 2 detachable cables. One in 1/4 inch, and one in 1/8 inch. Or choose two of one size. This model also has a built-in sound limiter for loud responses on large or near surface targets. It muffles the audio at that time to save your ears from painfully high db levels.
3) Killer Bee's----Worst noise reduction of the three. The threshold audio is close to the Grey Ghost's, and slightly better than the Timberwolves. This model has a toggle for the sound limiter unlike the Grey Ghosts. This can make a difference depending on the detector used. With sound limiter ON they are very close to the Grey Ghosts, but when its OFF you get a clearer & cleaner audio target response, especially on louder targets. They do seem to have a slightly cleaner sound overall as I had heard before buying them, however, the poorer noise reduction of the ear cups does not win me over. They are comfortable headphones, and if noise reduction is NOT important, these are a good buy.