Seriously,
If your height is under 5'5 or the flight is under 4 hrs they are OK,
otherwise consider other full service airlines because if you fly with them long haul (over 6 hrs or overnight) and save couple hundred dollars you might be losing more than that because you will arrive at your destination very tired can't enjoy your holiday immediately....not to mention the possibility of getting a sore back, or got a cold because their A330 flights are ice cold !
Generally their really really cheap flights are only available for low demand dates anyway...