Musashi do a variety of different products, their supposed to be one of the better manufacturers. There's lots of companies that sell protein powders and other "build super muscles" products - many of them are scary when you read the ingredients list.
These types of products all "work" to greater or lesser degree but are heavily dependent on what else you do. The usual - exercise, remove junk food, eat the right kinds of food - in conjuction with the products can help.
But it's the "can" part which catches people out. If you have two people with the same starting physique, both do the same level of exercise and both consume exactly the same diet but one also has the supplement - it'd be interesting to see if there was a measurable difference between the two.
Though the muscle-bags they put on the posters / packaging are the types of people that spend 8 hours at the gym and weigh all their food anyway. So in that context you probably could end up looking like them - if you spend all day at the gym and obsess about your food. The product itself is incidental if your diet includes lots of protein from other sources.