My opinion below is based on information and experience from my crossdressing days, which are three years or more in the past.
That said, I've been around enough to have seen a few silicone body suits. About the only real advantage I see is the ability to achieve what is, from fifty feet away, a really feminine shape, and go back to being completely male afterward.
However, silicone does not breathe, and if you are anywhere warm, this can become a real problem in terms of trapping sweat and body heat.
IMHO, you are better off with a good set of forms, or a breastplate if you really want to go that far, a good pair of hip pads or padded undies, and a good spandex cincher for your waist -- which will breathe and wick away moisture if you get one of the better ones. You can also purchase the best breast forms, hip pads and waist cincher for less than half of what you would pay for a good silicone body suit.