It sounds like your expectations are right on regarding flying Allegiant. The majority of people who have issues with Allegiant do so because they're unfamiliar with the ULCC fee structure. I used to fly G4 regularly when I was a college stupid in LAS and didn't mind traveling with just a backpack as a personal item. I never had any issues with delayed/canceled flights, but its worth mentioning that you probably shouldn't fly them if you need to be somewhere at a certain time. Because of their much more limited route network and higher utilization on peak travel days, IRROPS can wreak havoc on your schedule.
To keep it simple, if everything works out, like it has for me, it can be an excellent value. But either be flexible or have a back-up plan just in case things go South.
Regarding the above safety concerns, these are certainly cause for concern and you should consider it when making your purchasing decision. If you search online you'll see that they lead the nation in mechanical diversions and emergency landings. They've also never had a fatal accident in their history, so to me, the risk is insignificant enough to fly them.