There are still very few peer reviewed studies on the effectiveness of MCT oil for weight loss, but there are some, and there are some more that use coconut oil. It would be a stretch to call these conclusions solid, but it appears that MCT oil may contribute to a small amount of fat loss for overweight men. We're talking 4 pounds over 12 weeks. For women results were even less certain. A lot more research needs to be done before it can be billed as a miracle cure. The best distillation of the research that's been thus far can be found here.
I'm still reading the research linked in this thorough analysis of Bulletproof Coffee's various claims, but what I have read makes a lot of sense. Anything that claims to give you a cheat code to bypass the old "eat fewer calories than you burn" method of weight loss is worthy of scrutiny. Bulletproof Coffee reeks of snake oil.