Well, they aren't terribly expensive to begin with. That's the good part.
Personally, I have not found "burn in" to matter in any equipment I have ever owned, but that has been MY experience. Obviously, YYMV. 250+ hours? That is definitely a downside, to me.

Just discovered these are the same as the Urbanears brand:
http://www.amazon.com/Urbanears-00150609-Plattan-Headphones-Black/dp/B0030IY17C/ref=sr_1_1?ie=UTF8&qid=1367073077&sr=8-1&keywords=urbanears+headphone

They look very similar.......the only difference seems to be the Urbanears version has round earpads and the Marshalls are square. I haven't heard the Urbanears version yet so I can't confirm

I'd never burned in a pair for more than 48 hours. I've *heard* of burn in periods of 1000 hours but this was the closest I've experienced to that. Also, the 1st pair I got sounded great immediately with NO burn in so go figure.

http://www.headfonia.com/the-marshall-headphones-major-and-minor/
I've been into hi-fi for a while. Personally, burn-in, has never done anything for my equipment. Maybe I just don't have very good hearing and can't tell the difference?
Maybe I'm lucky and things have been good or bad out of the box for me?
LOL.