Literally thousands of people use off-site shuttles to go to and from Disney World on a daily basis. If they are on time and the schedule works for your party, they are a perfectly fine way to travel. You just need to look at it as mass transportation, which always comes with some negatives.
People value different things differently. Some people will accept the fact that it takes extra time to reach their destination (most likely with transfers) if it means not spending hundreds of dollars to rent a car and pay for parking. Other folks feel differently.