Just quickly read about the Alli diet...
Kinda neat that they can sell something that makes you crap your pants if you cheat on it (much better than just getting queasy).
Unfortunately, your body NEEDS fat to burn fat - just not the vast quantities of transfats that most Americans base their diet on. Keeping the macronutrient balance between protein, carbs, and fats is what makes your body run efficiently.
As far as Sensa...
The list of ingredients says it all. All the ingredients listed on their website are chemically-derived, or are huge insulin triggers. Despite whether it makes you lose any weight (presumably by making you feel full), it is about as healthy for you as drinking a can of soda.
You COULD spend money on all of these weight loss programs and gimmicks; or you could just eat sensibly-sized portions of food (lean meats, fresh veggies, fresh fruits, berries, nuts, water...) three to five times a day. This is the kind of diet that will make you lean (normalize your metabolism to get you to your genetically-designed body composition) and healthy (eliminate insulin-driven diseases, reduce your potential for cancers, etc.).