In my opinion, it wouldn't. The whole point in the first minute (After cells open) or so of Jail Break is to disarm terrorists and get them to the correct location. Granted, I can see how the vests would be fun, but an entire team would be crazy. The costs would have to extreme and limited to no more than 1-2 per round without the ability to purchase more.
Also, I believe that it should be an instant kill should you be found having one. It needs to be visible in some way, but being overly visible is like a death sentence. This can also lead to JUMPY CTs who shoot someone who doesn't have it.