While these certainly work for their marketed purpose, I find these nylon dust covers especially useful for microphones. This way I can leave them on the stand without worrying about dust collecting on the diaphragm.
I'm pleased with the size and muted branding on these, but think the nylon is rather thin and flimsy. Comparing them to a set of otherwise identical headphone bags from OnStage, the OnStage are noticeably thicker and better quality. That said, I have no doubt these will work just as well at keeping dust away.
If the goal is protecting headphones for travel, I would look at other options.