I used it, not S4 but Ostarine.
I think it was too low a dose. 20mg ED. Though, my Nutz came back ok and I held muscle, but I was in the WORST mood ever for like a month. I usually sail through PCT without problems. In fact, better mood than when on gear and better libido.
If you want to use something only slightly suppressive and free up some test, I'd go with good 'ol Proviron.