I have talked to many who have flown on Allegiant Air. Very few complaints. Many passengers have complimented the airlines on the seats and the courtesy of the employees. The direct flights are great and it seems like Allegiant pretty much keeps to its schedules. Many like going to their smaller airports closer to their home towns and the less passenger traffic they have to put up with.
The only drawback is Allegiant lands 30 miles farther from the Disney, Sea World and Universal properties and there is no DME to the Orlando Sanford International Airport. So you have to find your own transportation. You are just going to have to set aside about $100.00 each way for car service or taxi. The shuttles from there are really taxis in that they don't leave until they have a minimum number of passengers, which will gross them $100.00 each way. The rentals run you about $200.00 to $400.00 per week.
In other words, plan your ground transportation ahead of time. Actually the taxis on the stand run by meter and the rate to Disney on the meter is about $110.00.