You won’t get very much added gains so to speak from 200/week directly from the mass. But there is many other benefits of masteron besides as a pre-contest steroid which when it’s used for that it’s usually ran 400+ generally in the 6-800+ range.
Benefits you will get from 200/week
It lowers shbg allowing for more free testosterone, it act as sort of an AI, it hardens your muscle, it can raise your libido, it’s androgenic which will help in a calorie deficit or bulk by blocking fat storage.
Down sides it can cause anxiety, its a dht derivative if your prone to male pattern baldness masteron will speed that up, and for some people it can have negative effects on lipids, and acne from the androgens.