I have never tried Weight watchers but used to go to Slimming world. I ended up putting on weight, though it was before I was type 2, they encouraged to eat chips and potatoes, even bread and for me I have found they spike my levels very badly. I gave up because I thought why should I pay 5 pound a week to be weighed to put weight on.
Since then, I have done my own way of dieting and have lost 7 stone though I have put a half a stone on but that was my own fault. I go to my doctors surgery once a month to be weighed and that is free.