From reviews I've read they're just normal Rotos 66s with a black coating which, according to reviews, is prone to wearing off. So they are essentially "less expensive" Black Beauties or Auroras.
At first I thought they were Tapewounds due to the wording "coated". Not the case. Rotosound are producing well priced tapewounds.
https://www.stringsdirect.co.uk/strings-c1/string-sets-c865/bass-guitar-c34/rotosound-tru-bass-flatwound-rs88ld-bass-strings-65-115-black-nylon-p799?gclid=Cj0KCQjw2NyFBhDoARIsAMtHtZ6pBbV-qAJIRRArikZ5ZRV-WwxR7CJcYs1OO24wzffLZgMmFa1NKDAaAiPQEALw_wcB#fo_c=1949&fo_k=4b58082cbb4dd65feb18ed9194ed8d28&fo_s=gplauk?utm_source=google&utm_medium=cpc&utm_term=
There's nothing revolutionary about the Nexus range - except maybe the price.