Some of you may remember the infamous Cone of Silence from the Get Smart comedy series made in the 1960s. In the show, the cone of silence was meant to provide a, well, cone of silence around two people who wanted to have a private conversation, like when discussing top secret information, so that no one outside the cone could hear them. The cone never worked correctly in the show, which is part of why it was a funny prop.
I’ve often wanted, or rather maybe needed is the better word, my own personal cone of silence. Since I, in part, make my living by writing, e.g., computer code as well as prose, having my own personal cone of silence around me so that I can read and write without having my thoughts constantly interrupted is critical to being productive. Moreover, sometimes, like when on flying in a plane or staying in a noisy hotel, I just want to tune out my environment. And finally, when mowing the lawn, I’d like to continue listening to my audio books or music without damaging my hearing.
Those were my criteria, and after using the Bose QuietComfort 15 Noise Cancelling Headphones, 
The headphones work best at filtering out, say, engine-type noise. I can listen to my audio books while mowing the grass on the tractor without having to adjust the volume. In other words, I use the same volume setting while mowing the grass to listen to my audio books as when listening to them inside the house. That’s pretty effective, to me.
The headphones do also suppress higher-pitched noises, like dogs barking or humans talking, but the headphones do not completely make those noises completely silent. Those noises are muffled, as if they were happening in another room.
As for comfort–I’ve worn these headphones for hours at a time and they did not bother me at all. I did notice that when I was outside mowing the grass, in the sun, that my ears did feel warm, but this was a minor inconvenience compared to the noise cancellation benefits.
The headphones come with a handy carrying case along with an audio cable to connect the headphones to audio devices as well as an airplane audio adapter plug. Also, they fold flat for easy packing. And note that there is some mechanical noise suppression from just wearing the headphones, but the noise cancelling function is battery operated–one AAA battery (included) gives you about 35 hours of noise cancelling quiet.
Are they worth the price? To me, yes. The hours of productivity they have allowed so far are already worth more than the purchase price. So I guess it comes down to how much you value your time, what types of environments you can be productive in, and if you’ve always dreamed of having your own personal cone of silence.