I did the Maternit21, too. Easy way to get more definitive insight about the baby without the cvs or amnio - I hear that it is considered to be a likely replacement for amnio. From the research I've done on it, it looks to be quite accurate. I got a negative result, though I haven't seen the actual test scores yet to analyze how accurate they seem to be. My NTS risks were low, but I did Maternit anyway because I'm older, it was mostly covered by insurance, and I wanted to know the sex earlier than the 20 week US. Good luck to you!
There's no chance Materni21 or any of those tests (Harmony, Verifi) will replace CVS and/or Amnio. Those blood tests screen for only the 3 trisomies, which make up less than half of genetic defects. CVS and Amnio are much more comprehensive. If the concern is ONLY Down Syndrome or one of the other trisomies, then those blood tests are enough. But they aren't a replacement for CVS and Amnio.