A neighbor did the NEXTGEN upgrade at MCO and said that beyond a small hiccup with his passport, the CLEAR employee wanted a Driver's License which my neighbor does not have because he is in a wheelchair and does not drive, it was quick and easy.
He said that the CLEAR employee had to go with him to a different machine to scan his passport saying that the CLEAR supervisor said to keep the line moving DLs only unless there was a reason to scan a passport.
Not sure how scanning DLs only makes things go faster, but he was upgraded without any other issues and while he did not get the random ID check, he needs special screening anyways due to being wheelchair bound, so he had to wait a bit for a TSA employee to help him.