I don't have much experience with Primo aside from oral version 20 years ago. Masteron is a different story. It's more of a volumizer than anything else I have used. Pumps can be painful if you use to much. I can recall going up to 500 mg/w with 500 mg test/w and I would have painful pumps just walking 3 blocks. I think Primo is super clean with no sides and fairly anabolic if you can get the real deal. Masteron is less expensive and easier to get and not as often faked.