@burcidi-- Yes, I used one for about a month last year. I don't really recommend it because as you said, it messes up the digestion system. And it's not really something you can use forever to maintain weight because it can have pretty severe side effects.
Since it prevents pancreatic enzyme lipase from absorbing fats, anytime you eat fats, you get diarrhea. And you don't only lose the fat molecules but also the vitamins and nutrients that require fat to be absorbed. I think if this medication is used long-term, it can cause serious vitamin deficiencies. Not to mention the short-term effects like dehydration due to diarrhea.
I did lose weight during that one month I used a pancreatic lipase inhibitor. But I didn't leave the bathroom and had so much gas and stomach pain. It really wasn't worth it. I think proper diet and exercise is a much better and safer route to take.