I've flown with them 3 times. Everytime it was late departing, around 30 minutes twice and a few hours delay one time.
I would check the flights going into MCO. I ran the figures this time and it was going to be cheaper flying into MCO. After taking a cab, which is around $110-125 from WDW one-way, or renting (we did one-way, dropping off at Car Care Center) and that was one-way $80. So add that in to your already cheap airfare and it doesn't become so cheap anymore.
It would be if you were renting a car the whole trip. But we use Disney transportation to get around. It's very easy to get to Disney from Sanford. It takes around 45 minutes.
Everytime we flew with them, the plane was full. It was pleasant though. They raffled stuff off to pass by the time. Sanford is very small, so it's very easy to get around.