They and Lidl are horrific; I worked for one many moons ago and whilst they may have changed back then they flogged you to get every penny out of you.
They do pay better than most and they believe because they do so they own you, the hours and the grief you get is insane. I did it for 5 years, made a lot of money and then moved on and it's a pretty regular occurrence with them as, especially with a family, the hours they demand are a killer on a social life. People just burn out.
Young and ambitious and don't mind living the job to make the money, go for it. Older and settled I really wouldn't recommend it.