I've used them and pretty much the things that are said are true.
But Bad?? No, not really, just niggles. Long queue at airport, took 40 mins. I started queing while the missus waited for the bags... which took 25 mins anyway. Then you are obliged to take their 'all risks' insurance, or pay a €600 deposit... for €25 ish I figured it wasn't worth the hassle. It also saves then having to note all the little dinks and scratches on the car. Full tank of fuel was €80 I think, about €10 more than pump price.
The car was functional, not the best appearence (no hub caps for a start) but it's not a fashion show.
Car was 2 years old, a Ford Focus, with about 35k miles on the clock. All the air con and stuff worked.
But hey ho, you're in and away in about an hour.
You return the car in the multi storey opposite the terminal building, far corner on right from the entrance.