Haven't flown with them yet..first time in April. But, I have friends who have flown with them and they have all given good reports. Sure, there have been instances where things weren't perfect. With Direct Air, at least from our airport, there aren't nearly as many flights as one would like. so, if a flight gets cancelled, it could be an issue getting another plane in there quickly. I wouldn't book with Direct Air if I 'had' to be somewhere that day, or perhaps even the next. I have booked with them for over April vacation. We fly out on a Thursday, which gives up plenty of wiggle room before our cruise departure on Sunday.
Sanford Intl is a dandy little airport. I have flown in there in the past. It is very user friendly, and much smaller than MCO. It takes about an hour to get to WDW...a rental car is probably the best way to go.