I use Allegiant on a regular basis. I ALWAYS purchase the insurance in case something comes up where I have to cancel or change a flight. This has paid off more than once!
I fly frequently and so I'm familiar with the ins and outs of flying. Allegiant is a budget airline so don't expect any frills. I had a couple of past issues and although my hold time with customer service was long, they resolved my issues to my satisfaction. Just remember, you get what you put out. I have seen customers that are extremely rude to the airline employees and get nowhere!
For the most part, Allegiant is great for those 2-3 hour flights. Much longer and you'll wish you'd have paid that extra chunk of money and fought the traffic, construction, and lines at Sky Harbor.