NS-10 monitors were the industry standard. They were originally designed to be used at the consumer level in home hi-fi setups. Studios started using them as a reference, something that sounds like generic hi-fi equipment like a good home hi-fi setup. Auratone cubes were another step down from that, a bad stereo, hi-fi system, car stereo, TV, etc.
The Idea is to A-B against your good monitors when you're mixing. If it sounds good on NS-10s it should sound good on the end users low end Hi-Fi system.
Somewhere along the way there seems to me an undercurrent that these are a highly desirable piece of vintage gear, often without understanding what their function is. I've seen users buy these and use them in place of modern studio monitors which is a big mistake. That is never what they were used for in the studio.
If you were specifically looking for a pair of NS-10 and you got them for a bargain price then that is great. My comments are in no way directed towards you in any negative way what so ever, I think NS-10 are great for what they are designed for. I just wanted to dispel some of the myth surrounding NS-10s so someone reading this may not blow $700 on ebay thinking they're getting great monitors when really they're getting a pair of generic hi-fi sounding monitors to A-B against.