I've ran several cycles of ostarine. It is a great compound but don't get your hopes too high... you're not going to blow up like if you are on a harsh PH or AAS.
First cycle(of anything by the way) I gained about 3-4lbs overall, but lost some fat so it was probably closer to 5lbs of muscle. Bear in mind this was the first time so I had fresh receptors.
Subsequent cycles I gained about the same 2-4lbs with modest strength increases and HUGE endurance increases, although I was also supplementing with other ummm.... stimulants and that probably played a large part.
Anyway, while not drastic the lean muscle gains tend to stick around, and you get a great recomp effect while on, but its not as pronounced when you finish pct.