I've been on the generic (not the extended release, I take it twice a day) for about 3 months now, never did the name brand. For me it's worked well. The first 2-3 weeks it totally killed my appetite but it's come back, no worse then it was before though.
I started taking it to quit smoking and help with depression issues. It totally helped me quit smoking. The medicine as well as lifestyle changes has really helped with the depression as well.
Sometimes I wonder if I still need it as I mainly was taking it to quit smoking, which I've succeeded. But I'll definatly stay on it until the spring at least
Ultimatley you need to do what you feel comfortable with, you could always try it and if doesn't work go back to the name brand.