Did you mean hd25-1 vs hd25SP ?
If so, they're quite different, 25SP at half price use more simple headband, slightly different impedance, sound darker / bass heavy with little high frequency extension, and there's not much details. On the other hand HD25-1 sound very much like scaled down 580 with more forward mids. If sound quality is high on your preference, don't get the 25sp - they're primarily good for isolation, with quite decent sound.