NS10s are kicking around because they're unusually good at time domain performance. For instance, they have miserable bass not only because they're small boxes and smallish drivers, but because they're an infinite baffle design, which is significantly better for time domain performance than bass reflex. The enclosures also dissipate energy quite well, and it's well established that this contributes to being able to 'translate' mixes: you get a better sense of what's actually in the track using NS10s than you might with many 'better sounding' speakers.
They spotlight midrange with a presence peak right where the ear's most sensitive, and this is in part because the woofer is actually designed more like a midrange: thin paper, conical rather than curved cross-section, both of which also contribute to 'sounding bad' tonally while delivering energy more unforgivingly.
They're not really about mastering, though, they're about mixing because if you have elements out of balance it will be screamingly, annoyingly obvious on NS10s. That's not down to their bad-soundingness, it's down to their ability to be incredibly unforgiving.
They spotlight midrange with a presence peak right where the ear's most sensitive, and this is in part because the woofer is actually designed more like a midrange: thin paper, conical rather than curved cross-section, both of which also contribute to 'sounding bad' tonally while delivering energy more unforgivingly.
They're not really about mastering, though, they're about mixing because if you have elements out of balance it will be screamingly, annoyingly obvious on NS10s. That's not down to their bad-soundingness, it's down to their ability to be incredibly unforgiving.