I've flown them 3 times. The planes are plain 737s, Southwest Airlines style with only coach. They are in OK shape.
If your a business traveler used to upgrades and perks, you wouldn't like them. If you just want the best price from point A to Point B, then they're fine.
Like any low cost carrier with only a few planes, if they have equipment problems on just one plane, it has ripple effect on their whole system.
Also, they are unlikely to put you on another carier, because as far as I know, They have no reciprocal agreements.
I would fly them again if the price was right. And I LOOOOOOOVE all these discount cariers out there who keep the evil cabal of the Big Six honest in pricing!
Mac
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Via con Dios!