Pros: Fun if you don't get hurt.
Cons: May cause severe danger.
In 1988 the top popped off my son's Sit N Spin and he fell backwards. The fall was so hard it caused him to go unconscious. I saw the fall from my kitchen window and my husband and I ran outside to his aid. Within a few moments he regained consciousness and I rushed him to the emergency room. A nurse in the emergency room told me that a similar accident had occurred to her child and she recommended me throwing away the toy.
It is now many years later and my son is still totally deaf in his right ear and has slight paralysis in his face. I am heartbroken over this and there is not a day that goes by that I regret letting him play with the toy outside on the patio. Had the toy been on carpet his injury would not have been so severe.
Note: I am not against all Sit N Spins as the only one I've ever owned is the one manufactured by Kenner in the late 80's. The top does come off pretty easily, and in fact while watching the the show America's Funniest Home Videos, I did see another child get hurt as well. A little girl was sitting on her Sit N Spin when the top came off. Fortunately for her, the Sit N Spin was on carpet so her injury was very minor.