Cynostane was one of those big prohormones that never panned out. It's very mild at best, and a lot of it seemed to be bunk. I'm pretty sure it got caught up in the last big prohormone ban too, so you'd technically be buying an illegal steroid now, and if that's the case, there are so many better options.
Also Patrick Arnold didn't like the potential for 3b - HSD blocking, found it to be troublesome -
"I found some information suggesting that 2alpha-cyano DHT (the unmethylated analog of the purported steroid we are discussing) is an inhibitor of 3b-hydroxysteroid dehydrogenase. Other steroids with this 2alpha-cyano have this potential as well, most notably trilostane
trilostane is used to block adrenal steoridogenesis (prevents cortisol and some other adrenal steroids production by blocking the essential 3b-HSD). Of course it also will block testicular steroidogenesis. But most concerning is the potential of adrenal insufficiency which can be life threatening especially in cases where some trauma happens to a victim.
So bottom line i think possible 3b-HSD inhibition is a serious potential concern with this stuff"