I would agree with the previous posters.
I would also add:
*you can save about $10 per ticket per person by going to the airport ticket counter and buying the tickets there, if that's convenient for you. (I guess I would call their customer service line --which is NOT toll free & can take FOREVER--to double check for your location & hours of operation), but for our family of 5, that saves us $100!
*Allegiant is about the only airline where you can get cheap fares last minute, providing there are open seats. They sell by what's open, not just raising the prices sky high 14 days out.
*Because they are a charter type airline, if the crew has been timed out, or there is a problem with the plane, you'll be at their mercy to get another plane/crew/whatever brought in from somewhere else. We've never had that happen, but my in-laws have.
*Their flights can be at crack of dawn in the morning. Ugh.
*Baggage fees will vary by location. Our location is $15 per way per carry-on, $25 per checked bag if pre-paid; much more at the airport. Your free "personal item" can be a backpack, small duffel, etc. Just has to fit under the seat in front of you (which has much more height clearance than the 7" bag depth they quote you, by the way). Hope that helps!