I tried both back in the day, and tech demo is exactly right (a really cool tech demo, to be sure! but still). The OS came with a simple task manager-type app that had two buttons on it that could be used to disable either processor (to demonstrate how it affected system performance, I guess?). Thought I, "Hmm, surely they wouldn't let you turn off both.." But nope; everything immediately halted.

By comparison, NeXTStep was quite polished, certainly by the time it was available for x86, which is when I used it.