Most passengers are well pleased with their flights in Allegiant. The advantage is that it is a non-stop flight of approximately 2 hours and you are in Florida. Both airports are small and real easy to navigate thru. The ticket price is also a big factor. Finding the right dates to fly and return are a little bit harder to do if you fly Allegiant.
DISNEY DME does not serve the Orlando-Sanford Airport which means if you book Allegiant Airlines you will have to pay for your transportation to DISNEY. If you want to travel DME don't go to Sanford. To many are making this mistake.
The disadvantages are the distance from WDW, approximately 50 miles, transportation to WDW, time and money, and the extra charges for the flight. Travel time from Sanford to WDW, in a taxi, car service or rented vehicle, is approximately one hour. You have a choice to guarantee the seat for each person for $11.00 per person per leg. In other words $22.00 for the round trip. It is about 1/2 and 1/2 as to passengers who guarantee the seat, which assures your family sitting together. If you take the chance and not pay the $22.00, chances are you will still get seats together. A car service will run you about $180.00 round trip to WDW. There is taxi service and that runs a little more than the prices you can get by contacting a car service thru the internet.
Some families have reported savings of $400.00 to $600.00 per family over the prices landing Orlando International, including ground transportation. A lot of families love going to their local airport and landing Sanford, which is another local airport, 1/10 the size of Orlando International. The time spent traveling to the local airport is worth a lot to many passengers.
All reports of Allegiant Airlines has been good. The service is friendly, quick and less passengers traveling for you to deal with.