I have read up on this airline, somewhat, but would prefer to hear from anyone that has actually flown it.
Comfort? Safety? Any other pertinent information you may know first hand? Thanks so much in advance.

I flew them from FL to Michigan once a few years ago. It was similar to AirTran, no frills but fine. The only thing I remember was the flight home being delayed but I can't recall why, if it was mechanical or weather.

Flew on this from South Bend to Orlando with kids and 2 grandkids. No problems at all, no delays. We will fly them again. They are convenient for us and reasonably priced. Another plus is that they fly out of smaller airports so there's not as much of a hassle with checkin.

What kinds of extra/hidden fees do they charge for baggage, etc?

$11.00 per person to RESERVE a seat one way otherwise you scramble for a seat. One carry on allowed, charge for checking bag is $10.00 per bag. Flex fee is $50.00, whatever that is!! These are prices for a Dec. trip from MSO to LAS. I emailed and asked what the flex fee was and got no response.
For full info,allegiantair.com

John..The $50 Flex Fee is the per segment fee to make changes.You change the outbound flight, $50..Change the return, $50...

Yeah, I just found the explaination on their site. Thanks

I've flown them twice in the past year from Knoxville to Orlando/Sanford and was pleased with what we got for the money. It is a no-frills airline and you have to accept that going in. That said, the flights took off on time, the agents and attendants were friendly and I like the fact they fly in and out of smaller airlines. After flying into Sanford outside of Orlando, I would never fly into the main Orlando airport ever again. I wish they flew more days a week from our city.

I love the fact that for the first time we have the option to fly at the last minute without paying $700+ per ticket and without having to stay over a Saturday night.

I will fly them again and do suggest paying the additional to reserve a seat.

We have taken it from Ohio to SFB a few times. No frills and as long as the landings and take-offs are of equal number they are doing it safely. People come from all over the state of Florida to pick up people arriving there. When a family can save 6-8 hundred bucks it is worth it for them.