Towball mounted racks - the good, the bad, the ugly. Please help me make the right purchase

[Dirt sweat and gears]

Im needing a ball mounted bicycle rack. Im trying to look at the issues owners has had to hopefully help guide me before making a purchase. I have a mountain and road bike currently with to many kids to count

 

1. Whats been your frustration or irritations! With a ball mounted unit
2. Do you get racks that can take more than 4 bikes?
3. How is the Back-up service/parts
4. Can one get access to your car if the bikes are loaded

 

Seeing that I’ve never had a bicycle rack hopefully this will help guide me in my purchase. Your input will be amazing. Thanks