Price...or so my wife believes because the price is without a seat assignment (I won’t fly without a guarantee of an aisle or window unless I’m with family taking the entire row) and before paying for your carry on. After those charges, it can still be cheaper than others but not by much. I can handle the 1/4” seat cushion for max of 2 hours, after that it’s torture.

I’ve never had a delay, but go with the average data that you can find online to see what it is likely to be for your flight.