I was on one in my last job. Been in this job for 3 weeks and whilst it's still only 12 hours a week, but also covering other shifts as and when - it IS 12 hours a week regardless of what everyone else is doing. So I know I will definitely have a minimum of £303 every 4 weeks.
The last job made me ill. Not only was it a joyous zero-hour contract but the boss seemed to hate his employees (or maybe just the female ones, who knows
) and the two women in my team and I were treated unfairly, spoken to like shit, and if we dared ask for a specific day off, berated for it because 'what if it's busy, do you see we have all these offers on, you have to work it's in your contract and on the rota'
Well actually zero hours and flexibility works both ways, technically. But fear stopped us ever saying that because we wanted to be able to pay the rent and eat. 
I remember a couple of years ago someone tried to raise a grievance against the store manager for treating employees terribly (and that was when we had a whopping 4 hours contract) - she was fired. And when I say fired I mean, humiliated, all of us interrogated about her with leading questions that we all struggled to answer without it being twisted to make her look bad, but no questions about the manager at all, and then the area and regional managers and store manager high-fiving each other after it was done, thinking they hadn't been seen. They deemed her racist for making a complaint, but the manager was never deemed sexist for telling women to go and cry in a corner and various other bile.
Like I said, in the end it made me ill and I was happy to escape to 12 hours in a supermarket(I earn more than minimum wage - by 2p, but it's still more and to me, it counts).
Horrible, horrible contracts. Sometimes now I have moments where I cry a little bit over how awful it was and wonder why I let it happen to me..

