Yup, I used them last July by booking a car through Economycarrentals. Was a bit suspicious at first as they were very new, however was pleasently surprised when getting booking confirmation. Did not have to pay up front fuel costs, just retrun car with same amount of fuel as it was supplied with and to top it all off the car was a brand new Renault Clio Diesel! Company is located off airport, but they provide a minibus to get you there, 5-6mins in total. They are based near IKEA in an underground car park to keep the cars clean and cool and i suppose save on costs of being near airport.
All in all I'd HIGHLY RECOMMEND this company, in fact I'm trying to book with them again but going through these comparison sites sometimes its difficult to get the company you want at a good price. Book with them, I'm a fussy bugger and I'd go back with them again and again.