I just got HD25-1s from B&H for no other reason than just unquenchable curiosity. After buying UM2s there really was no reason to get these but I bought them anyway. Sheesh.
Initial impression is there's a BIG low end--*maybe* too big, we'll see as they burn in--and bright across the rest of the spectrum. Although I very recently sold my K81DJ to help offset my UM2 purchase, and can't do an actual A/B head-to-head with them--the HD25-1 do sound brighter and more refined than my memory of the K81DJ. It will be interesting to see if I wind up finding the HD25-1 fatiguing as I do with Grados--they're quite bright and up front which is something I like very much but am not always able to take with my oversensitive ears. Time will tell on that. I would not say they have a Grado signature if SR60 and HF-1 (the only Grados I've heard) are any indication. These have WAY more bass than those Grados, and Grados start fatiguing my ears after 10-15 minutes which so far these do not.
The headphones are also MUCH smaller and lighter than expected. When I received the ship box, I actually wondered if I'd received an empty box (something that happens frequently with Sennheiser--and already to me once with HD650s). Of additional note, the Sennheiser box they came in was extremely flimsy though and the headphones did not arrive in plastic of any sort--I still wonder if I received a return or something. Nevertheless the headphones look *mint* and the cable looked machine-wound and tied so I guess I'm unsure.
As far as future recommendations to others go I still think it's hard to actually justify spending the $100 more for these over K81DJ from a value perspective, as I think they do have the same basic sound signature--big bass, etc.--but to say they're a notch better than K81DJ seems accurate. Although the bass is big they don't have the more artificial sounding "loudness on" signature that the K81DJ seems to have. I think they appear more comfortable to me than K81DJ so far but we'll see over weeks and months if I still feel that's the case. The value of the K81DJ is still hard to beat though if budget is a consideration--but if you use portable headphones a lot though you tend to want to spend whatever is necessary to get the best sound possible which I guess is why I bit the bullet and purchased them myself.
In any case, I am not disappointed. Will just have to soak them in over time and see if they maintain a permanent place in my collection. HD25-1 + UM2 seems to be portable overkill but at the moment I feel I'm keeping both. Mo money, mo money...