I have used A LOT of ostarine, and it is almost impossible to lose weight on that shit. Don't get me wrong you can lose fat on it and recomp pretty well on it, but I have only ever been able to lose like 2lb on it, it really makes you hold on to too much weight to lose 20lbs. Even when I force myself into a pretty severe deficit on it, I don't lose at nearly the rate I should, I hold on to all lean muscle and just lose fat, albeit slower than I should given the cals I'm getting.
Plus it makes me very hungry and cheat all the time, but you don't really put on any fat. It does the opposite for others and lots of people complain about nausea and bowel irritation. (on an unrelated side note, anavar also makes me hungry as fuck, so I think my appetite reactions to compounds are the opposite of most people)