I agree with owly. 700 calories of fat will make a woman or a small man gain weight, ketosis or not. The idea of eating-all-the-fat-you-want works well with big guys, young guys, or guys who work out a lot. Everybody else...gains weight. Bulletproof coffee/tea/hot cocoa is especially dangerous in this respect because it's a very easy way to wolf down calories without knowing it.
It's okay to start with salted butter IF you clarify it and use the clarified stuff in the bulletproof tea. All the salt concentrates in the milky layer and gets thrown out.