Class I anabolic. It works by binding to the AR and is used for muscle tone, cutting, etc. Very mild anabolic and women can use in low dosages. EQ would not be the best drug to stack with it since EQ is also is a class I anabolic. Stack Primo with a class II anabolic for best results which will put on muscle by all different means. Other class II drugs are: Winny, Halo, Dbol, Anadrol, etc. Also, Test and Tren fall under class I and II (the only two drugs that do so) and they are excellent choices as well.
I have used Primo once before. Good stuff and very easy to keep gains. The stuff is thick and you can "feel" it while injecting. Not really a sharp pain or anything but strange nonetheless.