Source: Macbook 12 with Audioquest DragonFly v1.2
 
Comfort and Construction:
 
Overall the comfort level was good to me for an in-ear monitor. The key is to correctly size the inserts. Cord length is good for this type of ear monitor. Ended into a 1/4” plug with a 45 degree angl. For use on an iPhone or iPod, this may be a slight distraction. The cord is sturdy. Seemed to have good thickness without being too thick. There are no controls on the cord. This could be a deal-breaker for some.
 
Sound:
 
Overall, the RE-400 has a good sound. The highs are crisp and detailed. The mids are solid. It does lack base, but most in-ear monitors will be the same. Isolation is good for an in-ear monitor. No active noise cancellation, but with a good fit using the correct inserts, the isolation is satisfactory. I was impressed with the clarity of these. Good sound separation.
 
Thoughts:
 
Easy to recommend if you are looking for a reasonably priced in-ear monitor. Good sound and comfort. Need to decide if the angled plug will detract or lack of in-line control forces another choice.

The Ziks have a great sound for Bluetooth wireless headphones. They can be wired directly if Bluetooth is not available. They offer a many features, including an innovative capacitive touch-control for volume, active noise-cancellation, and an app for smartphones that acts as a virtual control panel for the headphones. The rechargeable battery is removable and replaceable. Even though they are heavy, they are comfortable. On the outside of the right ear cup there is capacitive touch-panel for controlling music playback and taking calls. Swiping vertically controls volume, while swiping horizontally lets you change tracks. Tapping the panel controls playback, and allows you to pause music, begin and end calls. Another feature is a motion detector, which senses when the headphone have been removed from your head. When somebody talks to you, just remove the headphones and the music will pause. Put them back on and playback resumes.
 
There is a free Parrot Audio Suite app available that allows customization of the sound and check battery level. There is an option to turn the noise cancellation on and off, and also an equalizer to change the sound. Also, there is the Parrot Concert Hall feature, which plays with virtual space and tries to turn your surroundings into a concert hall or jazz club. It’s a fun to move some virtual speakers around. They have added a "Tuned by Lou Reed" setting that reflects the way Lou Reed tuned his headphones. 
 
If the battery is dead, you still can use them as passive headphones. Used this way, the music doesn't have the same punch, but it’s not really how the headphones are supposed to be used, and I really don’t recommend it.
 
They are not the best-sounding, nor best noise-canceling headphones, but they look great and are wireless!

My experience with noise-canceling headphones include the Bose QC-15 and the Parrot Ziks.
 
In comparison, the Sennheiser PXC 450s sound really nice. The sound is clear and revealing. Good bass, but not muddy. They will expose poor quality MP3s. They are very comfortable and can be worn for long periods of time without any discomfort. I think the Bose are slightly more comfortable, but not by much. They are a large headphone set, but they fold up for travel, and they come in a zipper case with a couple of adapters. They seem to be well built. The noise-canceling is not quite as good as the QC-15s, but the sound is much better. A fair trade. They are not noise elimination headphones. You will still hear (faintly) the sound of crying children on the plane. The battery (AAA) life is very good and they can be used once the battery is dead. A great feature. There is a slight loss of bass when using the headphones sans noise-canceling. Also, there is a talk-through button that mutes the music and uses the microphones to here the outside world. This is handy at counters and when someone is asking questions, but be ready for odd looks.
 
Some negatives: The talk-through button does not pause the music when used. Also, the volume controls on the headphones change the volume on the headphones, not the iPod. The cord is does not have iPhone controls. 
 
Since buying them, I think they will replace my Bose as my choice for travel. I use the Ziks mostly for walks around the neighborhood because of the wireless function. Good combination of noise reduction and quality sound. Recommended.