Note that there is no +/- db specification in the frequency response. There's your first clue.

One set could be down 4db at 50hz and down 15db at 12K and they'd still be able to state those totally useless specifications.

Even if the specs stated +/- 2db, you would still hear a difference in tonal quality. There are other factors besides frequency response involved such as damping and various types of distortion that can mask certain frequencies.

The only useful spec I see there is the impedance, which is 22 ohms. That means it will be pretty darn loud compared to many other headphones. I have an older set of AKGs which are 600 ohms. I have to crank the volume on my headphone output to get them to a decent level. However, any headphone with an impedance of 100 ohms or less should go plenty loud with just about any headphone amp.

You really have to try several and see which you like as far as the sound goes.