Gray said:
You prove the point about listening for yourself - I wonder how many people have compared £15 and £189 pairs when choosing.
As for durability, I'd expect the K550s to be every bit as durable as the Momentums. Like you, I've replaced earpads, headbands and repaired leads over the years especially on pairs given very heavy daily use, so I understand why you want durability.
I know nothing of the Californian Headphone Company you mention, but I think I know of a man who might.....watch out for a post from Dalethorn. If anyone can help you with headphone advice, he can.
Funny thing - I took a long look at the California headphone offerings a couple years ago, and decided against them. I don't remember exactly why, but somewhere between the reviews, the price, and the expected result, I didn't see the value. Sometimes if an item is unique I'll go for it, but after getting several pricy headphones that were meh for sound quality (NightHawk, Pryma, BlueMic Ella....), I decided to wait more and buy less.
I bought a K553 from Massdrop a while back, and loved them. Good build, very good sound, big enough earcups. If the original K550 is as good, they should be a good purchase. At this point in time, you should get a bargain price.