To the OP, so how did the friend change the rules of the game to make it not worth it? Did he inject carbs somehow?
And yes, if a fat-burner takes in more fat calories than fat calories are burned, he'll gain weight. Duh. The point is that a rea fat-burner won't WANT to take in all those fat calories. He'll be full, he'll forget to eat, he'll get sick, etc.
5'0" female, 44 years old. Started Primal October 31, 2011, at a skinny fat 111.5 lbs. Low weight: 99.5 lb on a fast. Gained back to 111 on sugar cheat. Currently fighting off sugar/candy cravings with bulletproof cocoa and a little rice.
I (try to) follow by-the-book primal as advocated by Mark Sisson, except for whey powder and a bit of cream. I advocate a two-month strict adjustment for newbies. But everybody is different and should tweak Primal to their own needs.