Very comfortable!
I'd got used to headphones that fit over my ears, because I found helmets that went round the ear uncomfortable.
Nevertheless, I was tempted by these headphones and I'm delighted.
They're very comfortable, and you can keep them on your ears all day without any discomfort (as long as you don't turn the sound up too loud, so be careful with your ears).
The sound quality is perfect.
However, I'm not an audiophile and this is the first time I've bought such top-of-the-range headphones that I've used in my life. The bass is a little more pleasant than on my previous headphones (another Sennheiser but mid-range).
On the other hand, they are very bulky and heavy, so don't buy them for mobile use.
I've had them for over a year now and I'm very happy with them.
The fact that you can change the jack cable is, I imagine, a positive point in terms of repairability, but as I don't move it around, it's not a cause for concern for me.