My mother ordered an Uber ride to take her from her home to Mayo Clinic. The first driver didn't show up so she called again. The second driver called John did come in a filthy car, took one look at her then said "I don't like you" and drove off. She called a third time and did get a very nice man who took her. This was Uber's second chance with us. The previous attempt also had the driver not show up at least once.
Neither of us will ever use Uber again as they have proven to be too unreliable. If you need a ride to a doctor's appointment it can't be a crap shoot if you will have a ride or not. If you decide to try them make sure you have plenty of time and patience to get to your destination and be prepared to find an alternative.